First you need to run all the Entourage updates, and make sure that OWA is working on the MAC and be sure you know the OWA URL. Then here are the settings in Entourage:
Server
Account ID = user account name on 2003 server
Domain= 2003 server domain name
p/w = user password
check the save password box
Exchange server=OWA URL (in my case with desktops I used the internal ip address , i.e. 198.160.0.3/exchange)
Check "this DAV . . ."
Do not check the override DAV port 443
Advanced settings
Public Folder = same OWA URL used above
Check is DAV . . .
LDAP server = again I used the internal IP, i.e. 192.168.0.3
Check the box for This server requires me to login in
Do not check the other two
This LDAP requires me to login
Override = 3268
How this helps you.