Big problem: with XP and 2000, you have to delete the partition containing Windows and reformat that partition before you can reinstall.
If all your data is on the one partition, you're basically screwed.
Download Knoppix, burn it onto a CD, and boot using it to at least see the contents of your hard drive. It may give you pointers as to what's going wrong, and if your hard drive's crashed completely, you won't be able to view any of it.
Master of common sense. If you don't like it, stop reading.