[arch-general] Skype locks up my system, not even sysrq keys work

[SanskritFritz]

When I do a videochat in skype, the whole system freezes after a
while. This while can be a couple to 10+ minutes. The system locks up
usually when I start or close some other apps in the background. When
it happens the screen doesnt change anymore, and the sound stutters
the last half second over and over again.
Nothing helps, not even the magic sysrq keys (REISUB), which otherwise
do work (tested it).
I suspect this could be a result of a new videocard in the system (the
problem started around that time, when I swapped the old GeForce 7300
GS to a new 8600 GT), but everything else works flawlessly, 3D games,
movies, compiz, everything, except skype. Is it possible that a
hardware problem causes a problem of this magnitude only with skype?
I couldn't find anything in the logfiles after reboot. There is no
overheating of the nvidia card or cpu, I constantly check it with
conky.
Later I'm going to switch back to the old videocard, and test, to see
if it is hardware related.
Please help me to find the problem if software related.
Cheers
SanskritFritz