By no means this reply is meant to outperform, impress or scare away the original poster or any other read. Just trying to clear some things. If it makes things even more unclear, please delete this post.
This is how it works on a domain:
To my knowledge if a user is created on a certain computer, it gets a unique identifier (SID). A user on another computer (other domain/workgroup/local computer), even if it has the same name, will get a different unique identifier (different SID).
For instance: When you delete an active directory item (user,computer, whatever) and recreate it, it will get a different SID. Since everything relating permissions and security is based upon the SID, and not the name, it will not work.
After some reading around i found out about Windows 7 homegroup:
Have you ever tried to share files on your home network but found that dealing with folder permissions and user accounts was just too frustrating? You arenâ€™t alone; the process can aggravate experienced IT pros and home enthusiasts alike. Just imagine how your parents feel when they try to share files across their home computers.
HomeGroup helps simplify file and printer sharing among computers that run WindowsÂ® 7 on your home network. Domain-joined computers can also join your homegroup, so you can bring your work laptop home and access your music collection. You can set up HomeGroup as easily as you log on to most password-protected Web sites. HomeGroup is a feature of Windows 7, and Home Premium or better is required to create a HomeGroup.