Mandriva 2006 + LAN + BT

I've got a 2 yr old HP Desktop (1ghz 256mb AMD) and an old old gayway Celeron that were donated to me for upgrading a coworkers computer. So I've been playing with Linux(FC4) on my main machine for awhile and now I want to make a dedicated server so I dont have to leave my gaming rig on 24/7.

I've got Mandriva 2006 on the Celeron, and have used iptables to foward packets to my main comp but BT keeps giving me NAT errors and I can only upload/download at like 500 BYTES when before I could u/d around 100-200 KB/s. Also I have two other comps on my LAN. Can you foward packets to them on the same ports or would you have to set different ones?

Also...

Should I use another version of Linux??
Whats a good firewall to use? I've been using Firestarter.
Should I strip the gayway and put the HDD and RAM in the HP and use it as the router/server instead and use it as a mail server or music streaming.

Azureus always gave me NAT errors even when i had the ports forwarded correctly. Not sure if you're using that, but there's always the possibilty of switching to another client. Once i switched to another client i never had it bitch about ports at all, and i had it set-up exactly the same as azereus.

Not quite sure what you're saying with the port thing, but i do know for certain that you can't have two or more computers using the same ports through your router at a time.