Totally agree with the above post.

I would suggest you keep your 8800GTS 640MB.

I've never liked ATI's move to the Catalyst driver set which forces you to install Microsoft's .net framework that ends up slowing down your whole computer.

I just don't like it at all. Too bad you can't change GPUs in laptops (x700 in my notebook).

I couldn't see why you wouldn't be happy with the card you have now. Multiple monitor and scaling support is, in my opinion, much better with nVidia graphics cards over ATI's and like people have said above it draws less power.

This is important because of the environment and well, you might as well add the price of a new power supply to the cost of the 2900XT since the one you have now could possibly be insufficient for it.

SOLID card all around and nVidia's graphics cards also have yet to see mature driver sets.

I'm not all too familiar with ATI GPU vendors, but nVidia's vendors usually have great tech support and lifetime warranties.

I suggest just using your videocard for whatever games you are playing now and see if it's "enough".

If not then step up to a GTX, but don't change it up for an HD 2900XT.

Cheers,
Mike