Current version is 1.05.00. I don't remember the arrangement of earlier versions. Forwarding should be there, but if you're going to be using P2P you should start by updating the firmware anyway. They've fixed quite a few bugs that affected security and the maximum number of connections. P2P clients use lots of connections.
The download page is here:
http://www.linksys.com/download/firmware.asp?fwid=183
If you've configured anything interesting it's helpful to write down your settings before the upgrade.