Take some time to remove old programs that you no longer use, and upgrade the programs and plug-ins you do use to current versions. In Windows XP, go to My Computer > Control Panel > Add or Remove Programs (in Vista it’s slightly different) and remove each program you no longer need. Maybe you have old toolbars and other things you tried out but didn’t like. It’s a good idea to just get rid of them here.
Consider getting a copy of Secunia Personal Software Inspector (PSI). This nifty program will look at all of your installed programs and tell you which ones are old and unsecure. PSI will also tell you what patches are needed on your system.
Get PSI here: psi.secunia.com