Hey AlanB, welcome to the forums and thanks for using OmniFocus!
It looks like Office for Mac 2011 is going to include a Cocoa version of Outlook, which means that Microsoft should (hopefully) add support for the "Services Menu" feature of OS X. OmniFocus uses that feature of the OS to allow you to select an email (or a text selection from an email) and "clip" the information into a new task.
It's incredibly handy, but Entourage lacks the necessary code to send that text over to us.
In the meantime, you might want to use a different OmniFocus feature - it can use Mail.app to read specially formatted emails and convert them into actions. (Check the "Processing Mail messages into actions" for the basics of how this feature works.)
Just set up a special gMail or Hotmail account that you forward messages you'd like to make into actions along to. It will work best if Mail.app will subscribe to that email address, but not your regular mail, and if Entourage does not subscribe to the special mail-into-actions account.