Good to hear its making some difference. As for drivers, I probably would just get the latest nVidia drivers. I have not really had any issues using those.
The latest ones on the nVidia site are: 93.71, released November 2006. So if they havent updated them for that long, I would think they were fairly stable.
In fact, they're the ones I'm using with my 7600GT
As for the power, if you dont get a little warning box popping up saying that the card is not receiving enough power, then you should be OK. I was actually using it with a 300W power supply, and didnt have any problems with it. Although my friend recommended I upgrade to a 350 or 400W unit.
However, he does silly things like run 4 HDD's, 2 Optical drives and 4 or 5 case fans in his box, so he needs LOTS of power (his new machine is going to have a 1000W PSU!!). I hate to think what his power bill is like... I only had 2 HDD, 1 Optical drive and 1 case fan.
Like Zolt says tho, a good PSU will bring all-round stability to a system. The key factor is its ability to supply constant voltages at high loads. Cheap PSU's dont, and it makes your system flakey, as when components dont get the required voltage they dont work so well... kinda like your lights dimming when there is a brown-out.
Anyway, feel free to test the card some and you can make a decision next week after you've had a chance to put it through its paces. I know I was able to peg it at a constant 20 FPS, even with crazy things like the NZAR scenary with (ugly) static aircraft. YMMV tho, so give it a good test.
EDIT: and yes... PSU's are just swap in/swap out...