Once you have installed the card and drivers, if you right click on an empty area of the Desktop>Properties>Settings tab>Advanced button>Adapter tab>(click on) List All Modes button, you will be able to see all the refresh/resolution/colour modes the card will support.
By highlighting the line with the required combination, you can set that configuration - ensure that Windows doesn't have to be rebooted for the change to take effect.
Thank you all for your comments. I want the card to be able to run First Person Shooters at High settings without stalling because the screen updates. I note that Stuarti says any size but Robo1240 says 24 inch max ??? who is correct?.
I should have mentioned that my current PC has a 8800GT and an old 19 inch monitor, not even widescreen. I just want to know the largest screen i can buy which will be able to run FPS at native resolution without any graphical problems. I had aproblem with Far Cry with an old graphics card