Try booting a Linux "Live" CD like Puppy Linux or one of the other bootable CD packages like EBCD, UBCD or best of all, UBCD4WIN. See if you can access your drives. If yes then you can move data from C: to another drive to make some room.
See this post by Happyrck on GeeksToGo for Puppy Linux:
http://www.geekstogo.com/.....=findpost&p=1197721#entry1197721
Get the latest version available as the one he recommends is no longer easy to find.
Ignore the stuff about saving data, you just need the info on downloading and creating the Puppy Linux bootable CD.
These two are iso images you download then use your burner software to create the bootable CD from:
EBCD
Ultimate Boot CD
This one you have to build on your system and you need a Windows XP Home, Pro or MCE CD. Takes a bit of work to set it up but it's not difficult and when you boot it, you have Windows XP:
Ultimate Boot CD for Windows
How to build UBCD4WIN