you want to get the install file saved to your pc then disconnect from the internet and disable all your security programs prior to doing an install. You can do the install in safe mode which will assure that only the basics will be running.
if you experienced problems with an earlier install of sp3 you likely will still experience that because sp3 has not changed in any way it is still the same.

I suggest you review this thread from here, I provided the links you will need and the links to what to do to prepare for the install.
Service Pack 3

and if you have a problem after the install do not do a system restore instead go into control panel add remove and remove sp3 from there. Doing a system restore will cause you to have a mix up of sp2 and sp3.

However to address your statement about IE8 it definitely will install with xpsp2 you do not have to have sp3. As you can see here on the install page for IE8 where they list the system requirements
Supported Operating Systems: Windows XP Service Pack 2; Windows XP Service Pack 3

Raven-

Thanx for showing me SP3 was not necessary for IE8. Guess I didn't read that site closely enough. My interpretation was the SP3 was necessary so thanx for showing me it wasn't.

I had done the search with IE8 and read all your posts and others as well as all the MS site stuff before posting the above. I went ahead and installed IE 8 w/o the SP 3- seems to be functioning properly; no comlaints so far. Works just fine. Not only that I can open PDF files online - not so easy with chrome.

I still can't figure the "install file" but simply haven't time to persue it.

My interpretation was the SP3 was necessary

It is necessary!

I think there has been a bit of confusion or communication problem here:

Important notice for users of Windows XP with Service Pack 2 (SP2): The support for your product will end July 13, 2010!

To ensure that you will receive all important security updates for Windows after that date you need to upgrade to Windows XP with Service Pack 3 (SP3) or later versions such as Windows 7.

It's also possible That IE8 May need to be uninstalled before installing Service Pack 3. See below:

After you install Windows XP Service Pack 3 (SP3), you cannot uninstall Windows Internet Explorer 7 or Internet Explorer 8.

When you use the Add or Remove Programs item in Control Panel, there is no option to uninstall Internet Explorer 7 or Internet Explorer 8.

Note This issue does not occur if you install Internet Explorer 7 or Internet Explorer 8 after you install Windows XP SP3.

"Thanx for showing me SP3 was not necessary for IE8"
they thought they had to have sp3 on their pc just to be able to get IE8 which is wrong IE8 will work fine on an sp2 machine.

mxyplx you said
"I still can't figure the "install file" but simply haven't time to persue it. "
in my post which I linked to I provided the link to the sp3 down loadable file. If you review those links you will find exactly where to get the file which you will download to your pc and how to use it and the directions for preparing your pc for the install. it is NOT from the windows update site it is from a specific site for the down-loadable file for sp3. The link I provided also gave all the info that zep mentions above in them and all the precautions.

one reason some browsers make it difficult to open pdf files online is that is an extremely dangerous thing to do, it can trigger hidden scripts which will then install malware on your pc. It is a much better habit to download any pdf file and scan it fully with your AV and malware programs prior to opening it. It is also why keeping the PDF reader you use such as Adobe fully updated at all times is essential. Many of the most serious vulnerabilities recently have been through PDF files and reader.
More on PDF Dangers

Near as I can tell I should:

Ignore the SP3 currently residing on my computer because I don't see any way to remove it safely.

Download and save the stand-a-lone SP3 37 minutes - no sweat there

Hope that it will download w/o installing b4 I can cut the internet's throat.

Remove IE8 via add/remove

Cut Avast and Zone Alarm and the Internet's collective throat.

Install sp3 - presumably that is possible by clicking on something

Re-install IE8

Fire up Avast, Zone Alarm and the Internet

Never open pdf files via my recently updated Foxit Reader or PDF Viewer on-line again as long as I live for ever and ever so help me Hannah.

or

Remove IE8 - will it revert to IE6? or at least somethhing I can connect to MS with?

Throw caution to the winds disable Avast & Zone Alarm & spyware Blaster

Go to windows update and let it install the SP3 currently on board as it sees fit

Enable Avast etc

Reinstall IE 8

I would not do the one through windows update and go online with out the protection especially since you said you had a problem with it when doing it that way before.

The stand alone file you simply select to download it to your pc, to like your desktop or where ever you choose, then once you have the internet connection disabled and have your security programs off then go to where you downloaded that file to and double click it to begin the install of it.

Yes you can remove IE8 through add remove before you do sp3 and it will go back to IE6, then as soon as you are back online (with your security programs back on) from the install of sp3 go immediately to your windows updates site and get any other updates and you should be offered IE8.

the guidelines link
Windows XP Service Pack 3 (SP3) Installation Guidelines

where to download the stand alone sp3 file from, click the download button and save to your pc, ignore any info there saying it is for IT professionals and not for single pc, this is the only download and is the one everyone uses when not doing it through windows updates.
Windows XP Service Pack 3

as to foxit reader, it is a much better choice than Adobe but you do have to make sure it is always updated to the latest version because it also has been targeted by the bad guys. Opening pdf files online has always been a bad habit that is not something new but now more are hitting it with some bad exploits. So whether or not you choose to continue opening them online would be up to you. Since you have foxit now have you removed the Adobe Pdf reader? if not you do still need to keep it updated because having any program on the pc that has not been updated can be a security risk.

Adobe is years gone.

Thanx for all the input I know it takes time/effort to type all that up. Here's what happened:

Well I did every nitpicking picayune time consuming thing that was recomended plus a couple other things that weren't: backup, scans, even uninstalled ZA and disabled other stuff and after all that it got a little over 1/2 way thru installing SP3 and quit because "Access is Denied" and something about SP3 setup error. No clue as to what stopped it.

I then went barefoot to the MS site and tried again - same result. I tried a 3rd time some other way (with ZA and Avast enabled this time) - exact same result.

I'm wondering if the Malicious Software Tool should have been removed too. Anyway it's over. Heck with it. I see from the MS site that XP SP2 support is "Ongoing" - no time limit stated.

My Computer > Properties shows SP2

Belarc Advisor shows SP3

Windows Update shows SP3 on board but not installed.

I type SP3 into search and it coughs up a big bunch of files in Windows/Software/etc/etc and if I compare the KB files there with those in Add/Remove or Windows they seem to all be there (I did not check each one).

I've had it. All that took WAY to much time. I did not google the problem further nor will I. I will re-install IE8 and push along with what ever SPx IS on there till the cows come home.

In the mean time I will go to Office Despot and play with Windows7 - get used to it. Tried Mac and Linux and prefer windows. In fact I have linux on a backup machine if this one goes kablooy. W-7 will function on this machine at 32 bit but that'd be OK for whom its for.

wow sorry to hear that but you are definitely not alone, many people still have problems with sp3. Which is why I go to such lengths to try to help people understand the issues. So many people say oh just go do it nothing bad will happen, well bad things can and do happen! The ones that were lucky and had it install with no problems were exactly that lucky!

There is an end date for the support of sp2 it is in July.
You can order the sp3 cd from one of the links I provided and try it from the cd but it does cost.
sp2 will of course continue to work but will no longer get windows updates.