Entourage syncs with iCal via iSync, so what you are really asking for here is native syncing with Apple Mail's To Do list, via CalDAV, I believe. There are several threads here where it has been requested over and over, so feel free to add your voice to the chorus. Near term, I think you're out of luck, sad to say.

I don't think fms is asking for any iCal integration. What fms wants is to sync Entourage with RTM directly. That has nothing to do with Apple's To Do list. There is no sync capability with RTM and Entourage. What version of Entourage are you using? I have an idea I'd like to try.

I realize that is not what he was asking for explicitly. Nonetheless, Entourage syncs, out of the box, with iCal and Mail's To-Do, which does provide the basis for what he seeks. This has been requested on the forums previously, and no one has ever ginned up a custom Entourage-RTM syncing method, so my comment was to point out how close a solution could be if RTM ever chose to pursue the CalDAV syncing that has been requested umpteen million times here on the forum.

Let me add my voice to this 'next enhancement'...
If RTM could sync to iCal (or Entourage) then it would be the perfect to do application for the iphone and the Mac...
Very much looking forward to this..