Netmeeting through a linux Masq box

Does anyone have any experience using Netmeeting through a Linux =
(Mandrake v6.1) masquerade internet connection? My wife has started an =
online class at UoP and needs to connect to her study group via =
Netmeeting. I have installed and tested inside the firewall - works =
fine. But need to know if there is a specific port(s) that need to be =
opened to allow it to work. I appreciate any help.

Regards,
Donn