With non-multi threaded apps, you'll get more bang for the buck with the dual. It will have a higher clock speed for the money spent. As apps become more multi-thread capable this will lean towards the quad. If you plan on upgrading again in a couple of years, satisfy yourself with a fast dual.
dave
-------------------- "Yes, I know it's flat here. When the seeing is good you can stand on your toes and see Chicago...."