I usually clean out my hard drives every 2 or 3 months, unless someone really bad happens, then i reformat right away. I have everything that's important burned on a couple CDs and cleaned with multiple scanners to make sure i don't get anything infected. It's easier and quicker than scanning and defragging 120gigs, lol. Even if you're not a really computer literate person i have to give microsoft credit for one thing, they made windows easy to install. WinXP Pro is extremely stable, Home isn't as good, but not bad and when I had 98 there were problems to no end, lol. If you have any kind of business files or anything you want to keep on your comp it's worth the investment, don't want to lose anything important.
Good luck in getting everything sorted out.
AsylumX