Recently announced the conversion of halo2 to pc has been started but it seem to play this game when it is released you will need Micro$oft windows vista as it is being made specifically for it and will not run on any other version of windows fullstop. Some infomation on the on this conversion to pc is in the link below.
http://www.megagames.com/news/show.cgi?&idtype=pc&database=946&page=1&
http://www.megagames.com/news/show.cgi?&idtype=pc&database=946&page=1&