Crashing on Vista...

and, yes, i already have the update listed above.  the game runs great in single player, and it also runs fine in multiplayer if you start from a new game.  however, when i join a saved game in multiplayer (i'm not hosting), the game will crash within an hour of gameplay.  this is online only (i not on a LAN).

system specs:
AMD AthlonX2 4600
ATI Radeon 2900 Pro
2GB DDR2-800
Creative X-Fi Xtreme Gamer
Microsoft Windows Vista Ultimate x64