It's not an hardware issue, alright.
It can't be network as I stated above. It also can't be GFX/Sound because it's all the same. in spectaor or ingame mode.
This problem is unique to you. I guess it's some kind of windows configuration fuckup since you use an off the shelf client. Uhm, how about a different defrag version?
Could you try some of the older VM files?
You can find them here:
http://defrag.sockenbuegeln.de/data/bin ... es/defrag/Everything from 1.91.08 to 1.91.20 should work.