Well my specs won't really change how much more power the video card will draw with overclocking, I think the PSU is in the mid 300s. It's a Lenovo workstation with the standard power supply. It's running an x800 now which should not be drawing as much power as the 8800, but I don't want to try overclocking the 8800 if it will add another 30-50 watts to the power needs.
im running an 8800gts 640mb overclocked to 650 core 1400 shader and 1050 memory. Im running a 470w thermaltake TR2 and when running furmark the 12v drops to 11.8v (even when not Overclocked), suggesting the PSU is getting strained a fair bit. Id say a mid 300w psu woud not be enough. Can you list the full specs and brand of PSU? I think the 8800GT uses less power than the GTS.