My system is running slow
To give us / you a level playing field [?] follow the link, clean your system.
clean up PC here

When you have finished your new XP set up, and you are happy with the performance.
Run HiJackThis [HJT] to give you a base line to check off from, should the worst ever happen again ............ just save the log somewhere that you'll remember, and label it something OBVIOUS

Did you upgrade to XP ?
Or dualboot ?

If you upgraded, did you really clean the Bast**d out ?

Or did you just install over, and format the existing partition ?