Multiple Domain – Login for Mobile users

Is there a way to have multiple domains in the drop down list on the login screen? I have XP Pro, and Win2K notebook users who login to three diferent domains. The user ends up with three profiles, three desktops, three ‘My Doc’s’ folders…….
Its a PAIN!
I have overcome some of the problems, but would like to make the domain switching process less involved. If I could automate the joining the domain process, or make the list show three domains, that would be great.
Any suggestions?