Hard Disk Space Continually Dissappears

Lately my Dell laptop has been acting strange. It all started with an unmountable boot drive one day. Running a Windows repair and Checkdisk got me back into Windows, however with no hard disk space available. Any programs or files I tried to move or delete would not "stay gone". I'd delete something, close the folder, reopen it, and the file would be there again. After some work, I was able to fix that and start freeing up space. After freeing up 5 gigs, I went to sleep. When I booted up the computer the next day, it was back at 0 bytes free. Now, no matter how much I delete, over time, my hard disk space available reduces itself to 0. I've never seen anything quite like this before. Normally I'd say I've got some sort of worm or virus, but given a few other variables I'm not so sure. Any solutions or ideas are appreciated.

I heared about a virus that replicates in some file sharing progs where they open ports on your PC and use it as a server to host downloads. 100's and 1000's of files downloaded every day without you knowing. Uninstall ALL file sharing progs you have. Search your HD for any AVI, Mpeg, MPG, WMV, Mov files and see if they should be there. Be warned it targets porn sites so some content may offend. Turn off system restore, Make sure your anti virus is upto date, boot into safe mode and run full scans.