MN-700 and messenger

Hi,
I am having trouble receiving video conference through
messenger 6.1 since I have installed the router. Is there
something in the router setup that will allow these
features to work correctly. If I start the webcam feature
I can see the other person and they can see me, if I
start audio they can hear me, but I cannot hear them. And
the video conference does not work at all. Is this a
firewall problem from the router? The people I am
connecting with are connected to the interner (no router
or such) and no internet connection firewall.
Any help would be great.

Thanks
anthony