Can't chat through the wall of FIRE

Sir Macallot

Got a strange one here...
My i-Mac (10.3.9 all updates) has a USB ADSL internet connection which it shares with the rest (3 PB G4's) of my network.
The FW is switched on and the MSN ports etc. are open.
Still MSN, Adium, iChat etc can't get past the FW??
Internet works fine but chatting... :(

Have you allows the ports for incoming and outgoing requests? It might be that it's only allowing incoming requests through those ports but not outgoing. Check your firewall settings just to be sure.

The other thing that just occurred to me: Which firewall is turned on?? Is this the firewall on the Mac? Does your router/modem also have firewalling capabilities? If you have these capabilities on the modem/router, then you don't need Mac OS X's firewall enabled and you would have to allow the ports on the modem's/router's firewall.