Unfirewalling a firewall

Is there any way I can completely dissable the firewall in my Linksys router, but still use it as a switch/router? I hit GRC, and with the router running I had quite a few ports appear as closed, and one as open. I took the router out of the line, and tossed Zone Alarm on, and now all of the ports they scan pop up as stealth. I'd like to keep it that way, but I've got to give net access to a second computer fairly soon, but I don't want to run it through this one and into that one. I'd like them to me exclusive.

TIA
-Ben