This has been driving me nuts for a long time and I finally figured out the applescript for this so I figured I should share.
The script is:
This script assumes you have an exchange account and a folder in that exchange account you want to use.
If you want to use an archive folder that is a subfolder of another folder, you’ll want to tweak the script to say something like “to folder archiveFolderName in folder parentFolderName in Exchange account exchangeAccount” and add a parentFolderName variable to the top of the script.
Now all you have to do is save the script in: “~/Documents/Microsoft User Data/Entourage Script Menu Items/Archive\cA“
This will put it in your script menu and set the keystroke ctrl+a to “Archive”.
Enjoy!