NTFS Drive Change Partition

For some reason my c: drive keeps filling up. I often now (almost daily) find myself with 0 MB available on the drive. When this happens (even with uninstalling programs and cleaning using CCleaner, Cleanup, scanning with Ad-Aware, etc, and TrendMicro's PcCillin online) my computer erases things (like my preference files in FoxFire and my address book in Palm - I keep back-ups regularly). The c: drive after rebooting might show 2-4 GB but this can disappear in the course of a day. I have plenty of room on my D: drive and was wondering two things:

1. Might there be some type of worm/trojan/virus doing this to me?
2. Is there a way to re-partition my hard drive without having to reinstall all my software? Currently my c: drive is 14 GB and my D: drive is 18 GB.

Thank you.