To keep it nice and simple, when I run setup I choose dhcp - send ethernet address for the external interface. Then install the latest bpalogin, edit the bpalogin.conf file manually only changing USERNAME and PASSWORD, then MOST IMPORTANTLY:
#mkdir -p /etc/e-smith/templates-custom/etc/hosts
cd /etc/e-smith/templates-custom/etc/hosts
#mcedit 21hostname
add the following into this file
61.9.192.13 dce-server.nsw.bigpond.net.au dce-server
Save the file, then
#/sbin/e-smith/expand-template /etc/hosts
Now start bpalogin
#/etc/rc.d/init.d/bpalogin start
And create a symlink in run level 7
#/ln -s /etc/rc.d/init.d/bpalogin /etc/rc.d/rc7.d/S91bpalogin
Big Darren has some more info on his site reagarding the auth servers. Check it out here:
http://www.ozcableguy.com/cable.html#172