He's running slack 9.1 so rc.inet1.conf shouldn't be set up to handle wireless yet. The file you want is /etc/rc.d/rc.wireless.conf. You could also manually set it via iwconfig as suggested.
I've always found the default rc.wireless.conf to be on the bloated side and a little confusing. Here is what I ussually do.
mv /etc/rc.d/rc.wireless.conf /etc/rc.d/rc.wireless.conf.orig
# Then make this your new rc.wireless.conf
# Wireless LAN adapter configuration
case "$HWADDR" in
# Gypsy Cafe:
# Gwens Airport:
Leave the MODE uncommented always and then just comment/uncomment the particulars of each network where ever you might happen to be. Restart your network after commenting/uncommenting and that should connect you.