Wanted to add that I am currently running an old 17 inch flat screen but am also looking to upgrade to a 20 in or larger screen with the new GPU. So advice on any limitations of the setup would be appreciated.
22" has been the gaming norm for several years, I wouldn't recommend anything smaller than that. I would probably get the monitor first, then get a video card. Using a GTX460 on a 17" screen would do nothing for you really that the GT220 can't do.
For a low-mid range card like a GTX460, you'll need a 450w minimum with 24a on the +12v rail.