Microsoft Exchange Server


Our company is migrating to MS Exchange Server 2003. After the initial configuration I am unable to get either Entourage 2004 or Mail 2.01 to connect to the Exchange server. However using VPC and Outlook I am able to connect to the Exchange server. I am sure I am missing something however after hours of research I am still at square one on how to begin to troubleshoot this. I am running Mac OS X 10.4.1 on a G5 and have complete access to both the network settings and the server settings. Any help on how to proceed would be greatly appreciated.