built in
also my m0n0wall is Version 1.235.. dunno if upgrading would help fix it? i'm kinda afraid to upgrade and mess everything up.
Should work, I'm guessing you already have NAT rules to map ports 3478 - 3658 inbound to the PS3 IP Address?
If so, the next step is to go to Firewall / NAT / Outbound
Create a new rule with
Interface: WAN
Source: <your internal network range>
Destination: <leave default>
Target: <leave blank>
Portmap: Check the box for "Disable port mapping"
Description: <type in whatever you like>
Click Save, now you'll see the rule you created. Check the box to "Enable advanced outbound NAT" and click Save again to activate it.
Check to make sure your Internet is still working (check a website or two)
Fire up the PS3, have it run the connection test and enjoy NAT2 gaming