xlsx is the extension Xcel started using with Office 2007. You may have to upgrade Open Office to a newer version to open it but it should do the job.

any other comments?

Open office Calc the latest versions should open it. I use only open office on my computers now. You should update your OO to the latest version anyway it has more features.
Out of the box OpenOffice.org version 3 opens Microsoft Office 2007 documents
From what I have read OO calc will open that type of file you can not save as that type though I think.
Also you might try Google docs I think it will open them.
Google Docs Adds Docx And Xlsx Support
If you want to just change the file type to one that you can open more easily you can use an online file converter to do that. I use zamzar
Zamzar.com - Free online file conversion

i finally installed oo 3.1 and it was able to open the spreadsheet. now getting 3.1 and getting it to work, well if you are interested that was a real interesting adventure!

in case this helps anyone else i'll copy and paste it here. i posted this at the oo bullentin board, see link below.

this is the final resolution:

this is going to be difficult to explain but i have solved the problem and i have to admit i am impressed that i was able to do this!

here's what i did after i posted this -

1st, instead of going to the web i opted to open an application i had. i clicked on oo 2.4 and it opened a window. from there i clicked on a link to do the download, 150 mb! it took about 45 minutes. but i still had ver 2.4. i realized i had to open the installation file that mozilla was showing me and when i double clicked the downloaded .exe or php file it started the install and i knew i was on the right track. that took a good 20 minutes and i told it to remove the 2.4 stuff. when done the icon for oo 3.1 writer on my task bar did not work! there are now 4 icons the 3.1 version put on my desktop. only the "oo org" 3.1 icon would launch oo and it was 3.1 so i could now use oo. but the other icons for impress, calc, writer and the task bar icon for writer all failed to work, they'd launch a window saying that it could not find "swriter.exe", trust me this is pretty confusing stuff for me! so i could get to oo 3.1 but only using the icon for "oo org" 3.1 so i right clicked the 3 icons that gave the swriter.exe error and looked at the properties. all 3 were going to C:\Program Files (x86)\OpenOffice.org 2.4\program which shouldn't exist as i told it to remove the 2.4 software but it did not put the correct target address for the 3.1 programs and i recognized this as screwy. i looked at the properties for the 1 icon that would launch oo 3.1 and the target was exactly the same as the 3 icon's targets that were 2.4 but it had 3 in the address - C:\Program Files (x86)\OpenOffice.org 3\program\swriter.exe so i changed the target in the icons that generated the can't find swriter.exe error. by doing that the 3 icons on the desktop went from being a white backround to bright colors and a larger icon! low and behold when i click on those 3 and the icon for the writer on the task bar each one launches the correct software! like i said, i am impressed i found this and was able to fix it, i can't imagine anyone would figure this out it just seems too cryptic! heck i even was able to open the spread sheet that started all this! i hate messing with stuff, i want it to work. i am not all that pc literate and i worry that if i change anything i'll mess something up.

i have to admit this was NOT easy to do. oo does NOT provide a correct download/installation. if this happened to me it must be happening to everyone. so not only did this process fail to remove some 2.4 files but it loaded the incorrect target address for 3 icons (using the C:\Program Files (x86)\OpenOffice.org 2.4\program\swriter.exe address)! makes me wonder.....

Here is a link that might be useful: open office setup trouble shooting forum

I am pretty impressed with your troubleshooting skills, tjg911!
Great work!

Pam

wow never had a single problem installing OO myself. Sorry you had to do all that.

Might be better in the future for those attempting it to do a full clean removal of the old version then do a new clean install of the new version.
this is where I always download mine from directly
OpenOffice.org 3.1.1