Move Users from “workgroup” to “domain”

I have created an NT (4.0) Domain at an office that used to use a “workgroup” configuration, with no domain. I have installed a BDC at that office and have created user accounts, etc. and have the user authenticate to the domain. This is no problem with Win98 clients, however I have some WinXP clients also.
Since XP creates a “new” user now that it is authenticating to the domain, how can I have them logon to the domain, and yet keep their profiles (stored locally) EXACTLY the same? So theycan access all of their programs and settings exactly as before.
500 points for a clear and concise answer!!