Computer management and local groups

Hi Guys.

I have a weird problem here. I have Windows XP Pro machines setup in a
workgroup. I do a RUNAS on my MMC.EXE on my administrator computer
using administrator credentials (these administrator credentials are
the same on every computer) and remotely manage a computer using the
MMC from my administrator computer. I can add a user account remotely
just fine, but when I go to add the user account to a local group on
the remote computer it asks for credentials again? If I put the
administrator credentials in, the only objects it presents to me are
special groups. It does not present any of the user objects on the
machine. I can drill around to all the sections of computer
management, so the adminstrative credentials are passing correctly to
the remote computer.

Any ideas?

Thanks,
Adam