I would recommend first downloading a free anti-spyware program, (such as [http://www.safer-networking.org/en/mirrors/index.html|Spybot SD]) to try to clean any malicious programs off your computer that might be slowing things down.
Second, I would remove any unnecessary older programs which you don't use any more. If this is a Windows machine, you should be able to do this by opening up the Control Panel, choosing Add or Remove Programs, and removing ones that you put on there which you don't use any more.
If your internet browser is slow, you can [http://www.google.com/search?hl=en&source=hp&q=how+to+clean+temporary+internet+files&aq=0&aqi=g10&aql=&oq=how+to+clean+tem&gs_rfai=|clean out] your temporary internet files to help speed it up.