Overclocking your video card is almost too simple (being Nvidia), and can really gain you some FPS
With a registry add on called coolbits, you can increase your speed by simply moving a slider
http://www.overclockers.com.au/techstuff/a_coolbits/ has the key and a very good guide on how to overclock your Nvidia card/what to look for if it overheats, etc
I have some pretty extreme cooling on mine, but I was able to gain a few hundred points on 3dmark 2001SE, and it seems like I've gained 10-15 FPS with my Geforce 2 Pro
One thing that helped me, was to go to the overclockers.com forum and search for my card. I then wrote down every speed for that card (both on the memory and processor). After that I made a range (IE between 230mhz and 245mhz). I started at the bottom, and slowly increased the speeds until it either hung after 5min of extreme gameplay, or started to snow. Once I hit my limit, I backed off 3 mhz, and its been running smooth ever since (but your setup will be different, so don't follow exactly what I said)