welcome to LQ!!!
the standard way to do this on linux, no matter which distro, is to use iptables/netfilter:
http://www.netfilter.org/
this is one of the best iptables tutorials:
http://iptables-tutorial.frozentux.n...-tutorial.html
and if you want to take it a step further look at:
http://lartc.org/lartc.html
honestly i think a simple iptables script is a better option than the point-and-click riddle you've gotten into...
if you describe your setup someone here might even write a little script for you which you just need to execute to start sharing your internet connection...
good luck with your (GUI) configuration issue, sorry i can't be of any help with that as i've never had the pleasure of using Suse... i'm sure someone will be right along to help you... hang in there...