routing between separate subnets

[Eamonn Sullivan]

I need to set up a separate "public" wireless network at my house,
temporarily. My thought was to plug in the new router in one of the
unused ethernet ports on a computer running Dapper and route traffic
toward the other router in the house (the one connected to the
Internet). I don't want the second router to see anything on the first
network, just get routed directly out to the Internet. The four
computers in the house are currently on a wireless network encrypted
with WPA-PSK. I need an open network, on a different subnet (and
hopefully be able to fiddle with the channels to minimize
interference).

Is this possible and does anyone have any suggestions on a basic
how-to or software that someone exceedingly dumb (i.e. me) could
follow?

-Eamonn