XP has a disc clean up program it's in your accessories toolbox, it helps to get rid of a lot of old stuff.
I have the free version of AVG antivirus and they just set up a one time free utility for speeding up your PC, it sells for $29 a year. I ran the free one and it helped a lot.
After using one of those cleaner programs like Torsten mentioned, due to my ignorance perhaps it screwed up everything to the point I had to format and reinstall my whole operating system after everything else failed including system restore. This wiped out every old file in the process.
If you aren't sure what you are doing it's best NOT to, take it to a pro you'll be ahead in the long run, and it should come back clean without cob webs as well.
Play it safe.
Gabby