Cider,
Partition Magic is good software. We use it on our company's client machines (they all run XP SP2) and I use it on my home laptop. It works well and is very intuitive. However, take what I say with a grain of salt. Like Nihil said, you might try it and completely muff your computer up.
And like Nihil was recommending, CCleaner is a great tool to clean up the junk piling up on your system. There's also the Free Internet Windows Washer (not the fanciest tool but it works).