Do regular security scans, defrag your HDD, remove unnecessary programs from startup, download the latest drivers, firmware, BIOS, and perhaps using a cleaning utility like CCleaner.

Well, for game performance..
Like Razear said, defrag, remove stuffs, all sorts of that. But what I do is I clean my registry and defrag often, Disable anti-virus or any programs running in the background. Also there must be an option on your video card to adjust for quality or for performance.

And for the game itself, (If you dont mind the slight lowering of quality for your games) I would lower the resolution, lower the texture quality, and well disable any of the graphical additions, like hi-def shadows, fogs, smooth edges etc.

Performance over quality.

Pentium 4? ...
It's pretty old now and SLOOOOW
Improve performance by improving your PC I would say..

Try doing upgrades to your computer.
Get another bigger hdd. 500gb or 1TB
Get another 2x1gb ram.
Replace the old graphics card with a new 1GB GPU.
And maybe cooling might be a problem, so cleaning your case, and adding more fans will improve the cooling of your components, thus making it work more efficiently.

game Booster :D its free

Reinstall windows is a good idea. As for upgrading parts I would totally start with a new system. Regardless of the hardware upgraded the P4 architecture is your bottleneck.

ooh pentium 4 lol

Your bottleneck as far as gaming is concerned is your graphics card. If you can upgrade it to something a bit newer you would see a lot of improvement. The Pentium 4 may not be all too new but it is at 3ghz. In the game settings, if you set everything down to the lowest but keep it at your monitors native resolution, you won't notice the quality as much.

Game Booster not working properly.......

Im using amd phenom II X2 550 processor with 4GB ram DDR3....its really amazing speed......and excellent graphics ati............i want to know how to do overclocking on this processor.....its possible from 3.1 to 3.6.

Integrated graphic cards sucks.....

can u specify ur old computer specifications.....

Someone raised an old thread.. Only thing making his system faster is a hammer. ;)

lower graphics

Honestly, thats a darn old system, why not upgrade to something a bit cheap but good performance, these days you can build a comp for around 300$ pretty good for gaming atm.