If you let me know these details, I can tell you what which one will be suitable:
1. You PC usage - will you be playing any 3D games?
2. Your power supply make & model number or wattage.
3. The size & shape of your PC case (e.g. slim-type or low-profile cases will only be able to house low-profile graphics cards).
I know that a Asus P5K SE will accept PCI-E graphics cards, so that's one detail taken care of. G