Copy Profiles

My users have been using NT for a while, but for some reason when they were setup they do not log into a domain, they are part of a workgroup. I want to make them part of our Domain, but at the same time I do not want to expalain why the desktop haschanged, and why they lost their favorites in their browser. What is the best way to copy the profile over and make the user part of the domain.
Thanks
-Nick