The difference between an upconverted DVD and a HD signal is much greater than the difference between 720P and 1080P. That being said if you have a good processor 480P can look pretty good. Whether you will see much of a difference is going to be determined by the source material, whatever processor is doing the scaling to the native resolution of the monitor and the distance you're sitting from the screen. At 10' you'll notice more of a difference on a 50" TV than a 32" set for example.
If I were to get a new TV these days I would probably just spring for a set with a native 1080P resolution, however if I had a 720p set (which I do) I wouldn't rule out getting a Blu-Ray player.
Then of course there's the fun of HDMI and don't get me started on that.
