iChat server setup advice needed

We noticed that in 10.4 server you can set up an iChat server..

Well a few our students want to do video chat. I read that this is actually
a Jabber server .. Apple modded ..

Although I have managed to get it working on the local network I am unable
to get it working accross networks we can text chat but no video or audio.

Firewall???

We have unix firewall not os x server one

all machine behind it are NATed ..

the Jabber server is on a global IP address

Has anyone had experience in running video/audio chat with os x server and
can tell me how to do it .. ie ports to open on the firewall any mapping
needed?

Does all the data that people send when video chatting go through the os x
server like a middle man?? or once connected do the two parties comunicate
directly? peer to peer?

Is there a way to set up iChat server so people can make there own
accounts?? like some public jabber servers?

As you may see I am totally lost with this and getting a big headache ...

Any advice is very very welcome..

Many thanks

Marc