UT3 is causing a very strange bug on my PC: From the time I start the game, processes aren't able to close properly for the end of the windows-session. If I close a program, the window, if any, disappears, but the process stays with maximum cpu-usage in the task-manager.
Before anyone shouts "VIRUS!!!", once again: it only happens after I start the game.
Any idea?
The game also freezes as soon as I click anything in the menu.

My system:
Athlon 64 3700+
Nvidia 7900GT
2MB Ram
Win XP Sp2

Here's an example: