I will make my first post a gather for opinion. Currently I am running an intel qx9770 sitting on a intel dx48bt2 with 4gb ram. Currently I have a Geforce 9800GX2 installed and it is a *PIG*! I really don't play games, but want the fasted screen refresh under win7 running a pair of acer AL2216w's. The reason I say this thing is a PIG is because it takes 2 ATX power connectors AND it gets HOTHOTHOT. I know this thing is pulling some juice. Is there another geforce card that is a little more *green*?
There are plenty that are a lot more green. Almost any graphics card on the market will easily, easily refresh your screen faster than the monitor is capable of displaying, so I'm not sure why you got a 9800gx2 in the first place. Are you running any graphically demanding apps at all?
Agreed - a 7600 shouldn't have done that. Windows really doesn't take much graphically. I'd get something like an ATI 4650 or an Nvidia 9500 (I'd take the ATI between the two, personally). A GTS 250 (as recommended above) would work great, but it is somewhat overkill and needs a supplemental 6 pin connector.
That's not what you asked originally though. That is a gaming card, it is entirely unnecessary for what you are asking about. It will be a waste of money and electricity, not on the level of the 9800x2 but that card is simply insane for you purposes.
Almost any modern card should be able to handle what you are asking about. If you insist on Nvidia the highest I would really recommend is a 9500gt but an HD4650 is better and more power efficient for the same price.