Regarding sleep mode, it didn't seem to cut the power consumption much. I am using about 180 watts while the PC is on but pretty much idle. Sleep mode cut it down to about 130 watts. I am go to try the sleep mode built into WinXP. I think that will cut it down more.
I've replaced the stock cooling on my 4850 with a Zalman VF1000 and it is keeping the card quite chilly now. However, the fan plug is incompatible with the the connector on the card so I've had to plug the fan directly onto the motherboard. So, it can no longer automatically adjust the fan...