Joining XP Mode VM to the Domain

You will need to add Domain Users (or the specific domain user or users) to the Local Users group on the XP Mode machine.

And because the users are connecting via Remote Desktop Protocol (RDP) you will need to add Domain Users (or the specific domain user or users) to the Remote Desktop Users group on the XP Mode machine.

From:

http://thelazyadmin.com/blogs/thelazyadmin/archive/2011/01/03/joining-xp-mode-vm-to-the-domain.aspx

Joining XP Mode VM to the Domain