The official release of XP compatability library for halo 2 release date has been announced! I have had my doubts, but I have been waiting for this a long time now. It supposed to support multiplayer as well as live. Anyways, the release date is set for the 15th, however, there may be delays. This was originally supposed to be out in late july. Heres the quote from the site:
Quote Originally Posted by Falling Leaf Systems
Alky for Games - Free Edition


The Free Edition of Alky for Games is expected to launch on the 15th of August 2007 with full support for Halo 2. Support for Shadowrun will be added shortly thereafter.
There are also other tools out as well that allow further XP compatibility for vista applications such as the side bar, screen savers etc. The DX10 compatibility libraries for XP aren't set for release until this winter though... :/

Heres the link to the update.