The US Xbox site now has an official page up for their upcoming port of Half-Life 2. You can find it here and Valve's official, original site here.
There's also an extra page on the US Xbox site not linked that I got from the US Xbox Newsletter. You can find that here.
The release date shown is October 2005. At this point, since I wasn't blown away by the PC Demo, hate Steam, and didn't like how Valve's carried itself on with the PC version, I doubt I'll run out and buy it right away, though I will rent it. If I enjoy the rent perhaps I'll pick it up. If it's bundled with a port of the original Half-Life or Half-Life: Source (a redone version of the original that uses the Source Engine) that would be a good bit more incentive for me to get it since the original game is one of the best FPSes of all time.
My PC's over 3 years old, but it will run the PC version of Half-Life 2 well enough, however I've long since refused to purchase it as I will not use or support the use of Steam. That "content distribution" system is a piece of shit, violates Half-Life 2's own license agreement, and is illegal in certain parts of Europe. Valve's gone power hungry.