Mailbox Creation, Exchange 2000

We are a small company which has just split off from a larger group and have taken our existing computers along with the software. I have recently added new staff to using microsoft small business server ‘new user wizard’. Even though the create mailbox option is ticked, no mail box seems to be created and when I try to add microsoft exchange server to the new staff’s email accounts, I get the message ‘the name could not be matched to a name in the address list’. What am I doing wrong? I am sure it used to work! I have tried to get a book but it appears our software is out of date. Help!!!