I have a combo that could be of interest... though it is AGP. But, I also have a AGP EVGA 7800 GS 256 GDDR3 Ram video card to go with it.
The mobo is a EPOX 8hmmi-a (I have to look it up for sure.) micro ATX. I also have a socket 754 A64 3200+ Venice core. Combine that with the 7800 GS and it is a pretty formadable PC. The board supports sata natively (no extra drivers needed).
On top of that, I do have 1 gig of ram (two sticks of ram, DDR 266 2 x 512 Mb). I had all of it working together perfectly. I was able to play every game I tried very well, Enemy Terretory: Quake Wars, Oblivion, Neverwinter Nights 2, Rainbow 6 Vegas. It played WoW flawlessly on almost max settings (I think I used 4xAA and 8xAF, but everything ingame maxed).
I am looking to get rid of all of it, so let me know if you have any interest in any or all the parts. None of the parts are older than a year, the video card is about 4 months old (never OC'd, though I heard it is very good at it). The CPU has never been OC'd either, though it is supposed to be a champ too. I also have a stock AMD HSF to go with it.
But, I don't know how you feel about going AGP. The video card will definately blow your 6600 out of the water, though.