Migrating Exchange 5.5 to 2003 to new AD

Hi,

At our faculty we are running (still) NT domain with Exchange 5.5.This summer we are planning (force) to dismantle our NT domain and use central AD of the university. The central AD has already all user accounts for our faculty but with different user name, THE PROBLEM IS HOW SHOULD WE TAKE OUR EXCHANGE DATA TO THEIR EXCHANGE 2003? We can not upgrade our Exchange 5.5 to 2003 and let it run with University AD because user credentials are different and above all University has clustered exchange 2003.
Any advise, suggestion, white paper, links are welcome.

Shashi