Exchange 2000 & client contact folder

I have just upgraded my company to Exchange 2000 from 5.5. The problem I am having is that the users who had personal contact folders seem disconnected from them. When they are trying to email to someone in their contact folder they have to open contacts and cut and paste the address into the email before it works. I know I am overlooking something but I cannot figure out how to integrate the contacts folder back into their Outlook client. Any help would be appreciated!