I hope you realize 1080P is just a waste of money with a monitor that is only 24" big. You'd have to sit a foot away to notice any difference. Anything beyond that and you won't be able to tell the difference between that and 720p.
Defcon my personal recommendation is save up another $300-400 and just buy a decent HD TV. If you want to double that as a monitor you can hook it via DVI to HDMI. Plus you'll get a decent size. Sticking to your budget and your going to get a tiny screen.
The whole concept of HD is getting more pixels on the screen. The smaller the screen the less having a supported HD resolution matters. But the bigger you go the more the pixels stretch to fill the screen reducing image quality. This is where 720 and 1080P come into play.
The only reason computer monitors have such high resolutions with smaller screen sizes is because you sit a foot from the monitor. Try knocking back a video's resolution and sit 8 feet away and tell me if you can notice a big difference on your computer screen. You won't because your eye's simply won't detect it because your to far away for it to make a noticeable difference.
I've got a 42" 1080P TV and I generally sit around 6 feet away. I can notice the 1080P at this distance. The closer I move the more I notice it. If I move back another 4 feet you can't tell a difference from that and 720P.