the reason for the continuous updates are for security purposes, as they find methods of possible vulnerability to the OS they will put out patches for you to update the system with, if you choose not to do them then it is possible that your pc could fall prey to the vulnerability that the patch was put out to fix. Much like when you buy a car and they later have a recall on an item they find has a defect they send you a notice to have the car brought in for the repair so you do not fall victim to what ever it is the recall was for.
Nothing it seems is perfect and the OS is far from perfect and the bad guys are constantly looking for new holes and methods to gain access to our computers to use them for nefarious purposes, hence the constant need to do security updates, not only on the OS however but on all programs that are on your pc, it is wise to use the Secunia tool which will scan the pc and inform you of many needed updates to the programs on your pc. We all have to be very vigilant in keeping all of our software programs updated.
Secunia Online Software Inspector

Even if you buy a brand new pc it will immediately need several updates, Microsoft puts out security updates every month generally so since the pc was built till the day you plug it in all those that have been accumulating will need to be installed.

IE7 is coming standard with new pcs because it is the latest version of IE and is more secure than IE6, however you can still get IE6 it is available. If your pc has sp3 on it then no you will not be able to remove IE7 that was one of the specific instructions given when sp3 came out that if you had IE 7 on your pc you need to remove it, install sp3, then re-install IE7 or those options would not be available.
Personally firefox is a much better browser and I would suggest trying it, it is a good idea to have at least one other browser on the pc should the need arise.

this link may be helpful to you.
running multiple versions of Internet Explorer at the same time.

i have IE7 on my new lap top and it's no problem, i can't tell any difference in the two.. i disabled the defender, but couldn't tell you how now.

I agree that Microsoft tries awful hard to push it's agenda, especially on things like Net Framework and Silverlight. Personally I turned off all the automatic updates and select to install updates that I think I want (or need) through softwarepatch.com.
About removing IE7, since you don't have SP3 you should be able to remove it through add/remove programs and it should revert back to IE6. The MS instructions are at the link below.
I agree with raven about how crappy Internet Explorer is. It's the biggest weakness in all Windows operating systems due to it's use of activex.

Terry

Here is a link that might be useful: How to uninstall Internet Explorer 7

Gee, thanks guys,
I now have another way of looking at this whole business of personal computers.
Thanks also for those valuable links

I'm another happy FireFox user here. The only time I use I.E. now is when some site has a video I want to see and it doesn't work. Then I right-click and choose the FireFox add-on called "IE View." This way I have the best of both worlds, so to speak.