If your going to format your hard disk try and partition it so next time u need to format it u just transfer everything to one of the other partitions and only format C drive.
I have 80Gb into 6 partitions
C: System 10 GB = where i have Windows XP, anti-virus, Firewall
D: Programs 10 GB = all other software, like office, Photoshop, etc
E: Games 20Gb = just for games
F: Music 10 GB = only MP3's
G: Videos 20Gb = only vids, top gear, movies, etc
H: Share 10Gb = this is where i have kazaa, and bit torrent, and all the file i share and download to.
I usually do virus scan, scandisk and defragment every month on all the drives expect the H: Share as this one is always with stuff to download and delete. It does take a few hours but just do it when you’re not at home.
My system with this maintenance goes on for more than a year with no problems or crash's at all.
If u don't know to partition it use fdisk and search for the instructions on the web.
Just be very very careful when using it as it will erase all the data u have on the disk.
This is good because the next time your Operating System starts going funny u just need to format C: and everything else is safe
Hope it helps.