Netmeeting over Proxy

First of all, thanks in advance and excuse my poor english.
Well let go... I have a homelan with several PCs. The net has access to internet through a router, in which I map some ports to specific PC (see also edonkey, http/ftp server, etc), but now I'm interesting in netmeeting or others videoconference software, these types of programs need to communicate over some ports, it's not problem to map them, but the trouble is that only one IP can be mapped.

The result is that only one PC can use the videoconference feature.

And my question is: If I'll use a PROXY server to redirect all petitions for those ports (that videoconference program use) from all and every PC in the LAN, is this posible? PROXY software redirects these ports automatically? need to map these ports?

More data: I've installed some proxy servers to test it, but all of them only offers to map any port to one IP, and that I need is to map ports to all the IPs (LAN).

Thanks again. Muadib