I had no issue with joining to a Small business server 2008 - Under Authentication tab set Windows AD (NTLM auth), filled out the realm (same as Domain of AD server), PDC = wins server, PDC ip = ip of wins server (BDC's blank) hit save.
on AD Join settings used domain netbios and admin: "NETBIOS\networkadmin" or "NETBIOS/networkadmin" or "
networkadmin@domain.local" - sorry, can't remember which worked - and networkadmin password.
Went back to Authentication page and hit Join Domain
Hope it works for you.