Well I think the best way would be to upgrade the ram. Aside from that, then maybe you could configure some start up not to start unless needed. Defragment from time to time. Perhaps twice a month and basically disk checking will also help. If your using windows, you can actually go windows online and follow their tips and guidelines.
true, better to eat than to have a faster pc but memory is so dirt cheap these days...I'd offer myself to the former Gov. of NY just to get some decent RAM
What I do is I go to start then run msconfig I shut down all the processes that don't need to run on startup as well as other stupid programs running in the backround. It frees up alot of ram.