Hey. I bought Halo 2 for Windows Vista a few weeks ago. I've beaten it a couple times on different difficulty levels. So far, there have been no bugs that have been a problem. It's a good game. Halo rocks; on Xbox and on PC. As for Vista having issues with games, there's almost always work-arounds. Anyway, Halo 2 works fine on vista and most other new games do as well. As long as the vista computer has enough ram, and you keep it updated, most things will work. If not you can always google your problems.
Hope the opinions helped...