if you are stuck with a p3, best way to keep it fast is to do as little as possible on it. Go camping or something
Seriously though, I have a p3 - 866 here and all I have on it is msn, office2007, windows, and antivirus and it runs pretty quick. Its a bit tardy on the bootup, but it still runs. And all this from a board thats literally been caught on fire, and has multiple blow capacitors. Im amazed its still running. Tough SOBs those p3s are.
If you ahve something over 2ghz, I wouldnt be too worried about it slowing down, after all, your 4800+ is still only 2.4-2.5ghz
its just sucks cause im use to my dual and no sloe down/waiting for things
i can go on ocn,listen to music and play windows games