What RAM memory do you have ? A 6600 GT really uses all components to the maximum, especially the CPU, but 3.0 GHz P4 should do it. My advice is to do a fresh install of Windows, download & install the latest ForceWare drivers from NVidia, then run some benchmarks on your computer (3DMark 2003 let's say) and see what scores you get. Post here first with your Ram and we should find the solution.