I know its graft but have a read through of these items. They are not SBS specific but give a real heads-up on dod-dialling
http://www.microsoft.com/technet/community/columns/cableguy/cg1001.mspx
http://www.microsoft.com/technet/community/chats/trans/network/05_0621_tn_net.mspx
This one gives you the concept of the account naming if you use dod dialling.
http://articles.techrepublic.com.com/5100-6345_11-5297112.html
I don't have a running SBS setup currently so I can't test this for the moment.