[Brian]

Heh, it turns out that a couple of folks already went the AppleScript route with this.

The relevant scripts are in this thread; check the end of the thread for the leopard-compatible revisions of the script. One script takes any actions you have selected and adds them to iCal when you run the script; the other moves any actions you have flagged over.

If you'd like to add the scripts to your OmniFocus toolbar, RobTrew helpfully wrote up some installation instructions in this one.

There's also a script in this thread which will scan OmniFocus periodically, adding all actions in a particular context to iCal as events.