saving a profile when joining a domain

I work at a school and we can't afford a full time admin, so I am the closest thing to it. I am trying to deploy Win Server 2003 and have every computer join the domain I create. My issue is that some of those computers already have profiles and when I join them to the network and they log in with their new user accounts, new profiles are automatically created. How can I use the SAME profiles they were using before in their new domain environment? is there a way to port the old profiles into win server 2003?
thanks,