The 9600 GT isn't a bad card, it should play most games at 1440 X 900 (Never heard of 1440 X 480 lol, I'm assuming that's what you meant) on high settings. How much you can overclock it is dependent on the card itself, every card overclocks differently. What is your budget?
The 9600GT has 64 shaders. The GT 220 is the card with only 48.
Anyway, the 9600GT is not a bad card, but it's too expensive now for what it is. Considering they are around $90 you are better off getting a Radeon 4850 or nVidia 9800GT. The Radeon 4850 is around $90 and is much faster. The 9800GT can be had for less than $90 and is slower than the 4850, but faster than the 9600GT. Depending on what you paid for it, you may want to return it for something faster if you can .
Anyway, the 9600GT will play older games at high settings at 1440x900, but for newer games you will have to probably lower some settings.
For overclocking follow some overclock tutorial, http://www.bjorn3d.com/read.php?cID=1702 is one I usually recommend as it takes everything in detail. Make sure you stress after each pair of increases. If you get weird dots, squares or stuff like that (Artifacts) decrease with 10Mhz. Note: Do check your hardware monitor, as it shows the current speeds (While Gpu-z etc will too, hardware monitor is usually 100% correct where gpu-z may be not.)