Join a sbs 2008 domain using a current domain account

My understanding is that sbs 2008 now allowes you to use a current domain account (say SBS 03) when joining the 2008 domain as opposed to a local account. My problem is it dosen’t give me that option when trying to use //connect. It says to right click on the profile and uncheck don’t share and try again. This option does not exsist. I have searched and not only can I not find any solutions or white papers on how it does work, I can’t even find anything documentation that would indicate it’s suppose to work. Can anyone direct me to a solution or at least some documentation on the issue.

Thanks
Bob Wiggins