Bungie's confirmed suspicions that Halo and Halo 2 will be slightly shinier than the average Xbox game running on Xbox 360 - if indeed the average Xbox game does run on Xbox 360, although that's a separate issue.
In an update to mark Halo 2's one-year anniversary on November 9th, Bungie revealed that both games will work out of the box on 360 and that both will feature widescreen support, 720p (progressive-scan) support, and full-scene anti-aliasing to smooth over those jagged edges.
Says Bungie: "we didn't redo any of the old textures or geometry - this is simply the game you already own, running at a higher resolution. The results are not miraculous, but for owners of HDTVs (or VGA monitors with the appropriate cable) they are sweet."
Bungie also ran some comparison shots of the improvements, which you can find lower down the update.
Halo fans will want to check out the page for other reasons too, as it features a big look back at Halo's path to market.