It seems that if I set my admin password to something reasonably complex (ie includes special characters) then the simba server.log shows tons of bind errors such as these:

2008-03-21 10:29:25.444 DEBUG [util:164] [samba] pid 6966 (stderr): ldap_bind: Invalid credentials (49)
2008-03-21 10:29:25.445 DEBUG [util:164] [samba] pid 6966 (stderr): additional info: NDS error: failed authentication (-669)

However, if I reset the password to something simple that does not include special characters, then the install completes successfully.