MSN Messenger Hangs after couple of seconds

HI
I am running XP Prof and do have MSN Messenger 6.1
installed. When i do videoconferencing he is locking up
my system after a couple of seconds. I have set the "IP
passthrough" correct/enabled and my provider does support
Voice/video over IP. I received recently a new video card
under warranty thinking that the videocard was the
problem but that is not the case. Any other settings i
should tweak or certain "services" i should change.
Any help welcome.
Thanks
Ocean 16