Find message in Entourage Sent Items folder

Could someone please tell me how to write a script that searchs for a string of text in the subject line of a message in the “Sent Items” folder. I just need to check that it exists - don’t have to do anything with it otherwise
Any suggestions appreciated!!

tell application "Microsoft Entourage"
	set existsMsg to (messages of sent mail folder whose subject contains "foo") is not {}
end tell

Thats for that!!