Wow, it was easier than I thought - I'm still in shock
pre-config your router w/login & password (I did this from an XP box)
Setup SME as server & gateway (dedicated), choose the ADSL nic for external network ethernet driver, I chose DHCP (send account name as client identifier) for the external config, and provide DHCP to local network, and accepted defaults for pretty much the rest. Server re-booted, and the 'test internet access' was sucessful. Jumped on to one of the 12 XP boxes connected to the server and fired up the web browser and away it went

Another option is this thread:
http://forums.contribs.org/index.php?topic=16426.msg63570#msg63570This tested OK for me from SME, but one of the XP boxes lost the server so I thought it had failed somehow. That box seemed to lose its connection (would be the first one I jumped on!!)