Get the "Entourage Default" sound set from Sound Set Central.
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http://www.soundsetcentral.com/download.html?id=484>
Drag the resulting "Entourage Default" sound set from the Archive folder to
/Users/<Your User>/Documents/Microsoft User Data/Entourage Sound Sets/.
Then, in Entourage, go to Entourage > Preferences, and then go to General
Preferences > Notification. On the Sound Set pop-up, select "Entourage
Default" to restore the Entourage X sounds.