Problem migrating local user account (not listed) to SBS 2003 domainaccount using SBS Network Config. Wizard

Greetings.

I successfully upgraded a Vista Home Premium machine to Vista Ultimate
so I can join the machine to my client's Small Business Server 2003
domain.

Both the SBS 2003 and Vista machines are fully updated and patched. I
currently have seven XP Pro machines as members of the domain.

After a few stumbling blocks with IE7 security, I was able to run the
Small Business Server Network Configuration Wizard via http://<server
name>/ConnectComputer.

At the "Assign users to this computer and migrate their profiles"
screen of the Wizard, I can add one of the "Available Users" to the
"Users assigned to this computer".

But in the "Select the name from the list that represents your
previous user account" section, the Assigned User is listed but the
existing local workgroup account is not. The "Current User Settings"
list box only lists "--None--".

This has been the method used for joining the XP machines to the
domain. Is this broken in Vista? If not, any idea how to get this
working? I really, REALLY want to preserve the user's profile.

Thank you for your attention,
Jeff