Hi Andrew,
Thanks for your update.
Based on my experience, there is no specific attribute controls whether an account is disabled. If a user is disabled, his UserAccountControl attribute value adds 0x002. For example, if a user is a normal user and disabled, set the UserAccountControl attribute to 0x0202 (0x002 + 0x0200). In decimal, this is 514 (2 + 512). Please note: If there are many kinds of the users, you need to list different UserAccountControl attribute value for them.
For more detailed information, please refer to the following KB: http://support.microsoft.com/kb/305144
Best Regards,
Anna Shi