Apps sharing in messenger

Hi ALL!

Well, I have a LAN and ISA 2004 as Firewall. I also have Windows Messenger
5.1. I am sharing application in my LAN without any issue. But when I'm
trying to share apps through Internet it gives me an error. I've opened MSN
protocol on ISA and it seems there is all OK with allowing Messenger. At
least there are no deny entries for Messenger in ISA log.

On other side is FreeBSD firewall/gateway and it has a rule to allow all
traffic from an IP in that LAN. We can type messeges, can view video, but
can't start apps sharing. So where I can find some howto or white papers for
allowing apps sharing through Inet.

TIA.