Whats a good overclocking limit for PNY NVIDIA GeForce 7600GS 400/400mhz (256ddr) (agp) please!please! help!!!

Depends on your cooling, get a program called GPU-Z and monitor your gpu temperature while you overclock. Overclock with Rivatuner, it's best for Nvidia cards. You can also increase your fan speed, if you have a fan, with Rivatuner, so it stays cooler after you overclock. After if you think that your gpu temp. is enough then stop overclocking. How much you wanna push it is up to you.