start off by running a bunch of spy/pest/virus programs. then run a regisrty cleaner, then defrag then go to START-->RUN-->type in msconfig and go to start up. Turn off all start ups that you really dont need running in the background. Then go to services and turn off anything that says "unknown". If ya want, right click on my computer, go to properties-->Advanced tab-->Performance settings and set it to best performance.
You can also run optimization programs like RAM Booster or PC Booster. Or get some small Free RAM program.
Other then that, get more ram