What else is on your CPU? Having RAM, but an old school processor and out of date parts under the hood could be the problem too.
SPYSWEEPER by Web Root in my opinion is the best spyware to run. Very user friendly. Microsoft also has a BETA version of the one they have you can DL from them.
---If you have one now, try turning it off and not having it on. On an older machine, a Spy Search pgm, WILL slow your CPU down. It is constantly running to catch spyware. Might be better off, not having it running 24/7 and just checking on your own every few days.
The MSCONFIG mentioned above is a MUST DO. The clearing of files or disk defrag is not going to solve anything if it goes THAT SLOW. May help, but if it is running slow enough that you are posting on a board it is something else. Especially if your cpu is starting slow when you start it up. AOL is notorious for putting all their stuff starting up. Same with MICROSOFT (IE, messenger, etc). Music program like LIMEWIRE, etc will do the same.