Hi Dan,
How much memory do you have in your system?
Try quitting all opened applications and try receiving mails through
Entourage.
Still if you have problem try following troubleshooting steps.
Try deleting Entourage Preferences and Check.
Follow following steps for the same.
1. Quit Entourage if it is still running.
2. Go to the [OS 10 hard drive]:Users:[Your User
name]:Library

references:Microsoft folder, move the following files to
Desktop.
Carbon Registration Database
Entourage Preferences
Entourage Settings (10)
3. Drag the com.Microsoft.Entourage.plist from the folder "[OS 10 hard
drive]:users:[Your user name]:Library

references" to the desktop.
Hope this resolves your issue.