Has anyone had any voltage issues with the MSI NX6600GT AGP (model VTD128) or any Geforce 6600 GT graphics card? Ensured the graphics card molar connector is connected to a spare molar provided by the power supply (Antec SL350). The only other devices connected to the power supply are 1 DVD drive, 1 CD-RW burner and 1 7200 rpm hard drive. The system successfully boots but only goes as far as the log-in screen then the monitor display goes blank but not off. I believe it's possibly due to a voltage issue but per MSI minimum power supply requirement for this card a 350 watt PSU should be sufficient. The Abit IC7-G motherboard BIOS has the AGP voltage set to 1.5 volts. If I don't get a resonse by the end of this week I'll most likely go out and purchase a 550 watt PSU then post back on the results.
I can't say about 6600GT I'm afraid, but I did run a linux box with 6800GT. I've been a reader of SilentPCReview.com for some time, and what I understand a power in such a minimal system shouldn't be a problem, given that there would not be dual processors attached. Quite often the power drawn by systems you describe is much less than 250W.
I run 550W Antec myself, that I bought after having some stability problems (it didn't help with those, but something else did and I got a chance to silence it too so it stayed). In retroperspective, it was a bad buy because it did not help one bit. So I would recommend trying out another nvidia card first. Of course, that is not always possible.
I know that this may not be that much helpfull but with all the help you give out here, at least I can try. 
i actualy had the same problem with my one of my quaddro 1100
Quite true, after all, those chips do have multiple parts on them and separated functionality. Though _usually_ it seems to be all or nothing or visual artifacts.
One more thing that came to my mind was that while the power consumption should be more than adequate, there are cases (rare ones) where the current drawn by the system was too high for the PSU. One might be able to get away with it by using different molex connectors, depending the PSU.
I should stress that these are very rare cases and still the main suspect should be the video card itself.
We've built so many boxes, and one thing I've learned is not to look at wattage rating only. different power supply have different output for "3.3v", "5v" and "12v", while both are rated at 400 watts.
Intel has a wattage calculator for its servers, you can at least get a general idea how much each device's power requirement is.
http://www.intel.com/support/motherboards/server/sb/cs-010758.htmhttp://www.intel.com/support/motherboards/...b/cs-010758.htm