Defrag, run anti virus and programs like adaware and counterspy, ccleaner is good for deleting bits of left over programs and general tidying up. Also check what is actually loaded at boot up and disable what you don't need. Assuming its XP you have goto START RUN then type MSCONFIG click the last box STARTUP and this is a list of what is loaded up. Be careful with this, if you disable the wrong things its possible you can stop windows starting, if this happens you would have to start in safe mode and then retick what you had unticked. Make sure you know what you have unticked, write it down, and make sure you also know how to get into safe mode before you do this. I realise its a bit time consuming but you are better disabling one item at a time.