its at newegg. But that x800 only has DDR memory. 6600GT also supports FP-32 textures. Shader model 3.0 does give a slight boost in performance, but that's not why i would suggest the 6600GT over the x800... Right now, the best deal seems to be a x1600pro for around $129. They can be crossfired if you have two x16 slots, you would of course need a second x1600pro.
Roger