For Xbox purposes, it is almost irrelevant what resolution your monitor supports, because most games only support 640X480p, (480p) and almost, if not all monitors support that res. As for 720p which is 1280X720p (16X9) and 1280X768p (4:3), if you monitor can go up to 1280X768, than that is all you need for some High-def gaming on your PC monitor, you don't and won't ever need a monitor that can go up to 2048X1536p for Xbox gaming. Your 17" monitor will work great, as long as the contrast ratio isn't too terrible.