Halo 2 (previously Vista only) coming to Windows XP
 

alling Leaf Systems has announced that they will be providing compatibility software that will allow Halo 2, an exclusive Vista title, to run on Windows XP. If you order Halo 2 through their site, you'll get the compatibility libraries FREE when they're released (current estimate is July).

http://www.prleap.com/pr/77567/