it has been happening to me also, mostly in the server select screen... however, someone else posted a possible fix that seems to help me somewhat. In the initial configuration window that first pops up when you run the game, force it to run in single threading mode, or do it manually in the task manager by setting affinity to one core. I have a dual core opteron cpu and this let's me at least join a game, although then i will usually crash within 5-10 minutes.