parabellum,
To be honest, 23 inches is not anything that special (in terms of having to make special arrangements graphics card wise). If you were proposing to buy, say, an Apple 30 inch "Cinema Display" then you would.
Generally speaking on most relatively recent machines, you should be pretty safe all the way up to 27 inches (I've currently got a 27 inch Iiyama plugged into a six year old HP box at home, using nothing but the machine's embedded graphics processor, no external graphics card).
A quick Google suggests an Nvidia GeForce 7900 GS 256MB is capable of driving anything up to 2560x1600, and something like the 27 inch I mentioned above is 1920 x 1080 (admittedly probably running close to the limit of the embedded Intel GMA on the HP mentioned above ! ) , so you'll have an even bigger "safety margin" on 23 inches.
Famous last words, but I'd say go for the monitor and forget the card, unless you really fancy an upgrade.
Last edited by mixture; 22nd September 2011 at 07:42.