The patch/update actually would have been significantly easier, but hey, that's not an option at this point, right!?
My suggestion to you would be to backup your information and start all over. There is a lot of stuff that is toying with your system registry and incomplete uninstalls, etc that you would really need to start over.
So, how do you do it? Well, if Windows starts, you can take a DVD or CD and just burn all your docs, mp3's and what nots to the DVD or CD. You can also take a USB drive and transfer them to another computer. Point is, SAVE YOUR DATA!!
After words, take your system restore disks or use the system restore partition on your computer to format and reinstall your system. Don't take off SP2!!
If Windows doesn't start, then you need to use Ubuntu's Live CD to save data. It is less intimidating than it sounds. Just wander over to www.ubuntu.com and download the 32-bit version. Use a CD burning tool to burn the file to a CD and slip the CD into the drive. Once it's up and running you can burn CD's of your data or use a USB drive.
Hope this helps! If you have any more questions don't hesitate to ask:)