bf2 Works on vista apart form a few bugs,
You need to right-click on ur bf2 logo and click "Run as Admin" even if you are logged in as admin you must do this or you get kicked by punkbuster for inadequate (sp lol) OS Privileges. Also the built in VOIP for bf2 does not work on vista and no solution has been found yet ( well since i last checked a few weeks ago) i find this annoying as noone can hear my random Alien2 (Aliens) Badass quotes ....pfft
Roflcopter it better!! I find Halo2 works better in XP though.
And heres the deal, why would Oblivion work but not Halo? They both use the My Documents folder for saves.
Both Halo and GTA:SA don't know where to save to, so they hit an "error" and crash. The document folder pertaining to each game doesn't exist. It's like going on a road trip in Europe with a US map.