... in Entourage for Mac OS X from the American format 4/25/05 to 25/4/05?
Amazingly, Help was helpful. Entourage picks it up from the OS.
Help in 2004:
Change the date or time format
Microsoft Entourage uses your Macintosh system settings to determine how to
display dates and times.
1. On the Apple menu, click System Preferences.
2. Click International.
If the International button is hidden, click Show All
Note For help on using System Preferences, open System Preferences, click
Help, and then click System Preferences Help.