Hey Russ, sorry you haven't gotten a reply to this yet. I was just browsing old questions and thought I'd have a crack at it. Hopefully you haven't gone away totally yet.
I actually answered a question very similar to this, here's the answer. What you can do is set up this exact same metric, and run your report on the incident metric table such that the definition is Incident Touched, the value is your group's name, and the assignment group is the help desk. That would effectively give you a list of all tickets (without duplicates) that were in your queue at some point and that ultimately ended up at the Help Desk.
If you want a metric to measure tickets that were actually transferred directly from your group to the Help Desk, even if the Help Desk transferred it somewhere else after that, that might be a bit more difficult, but doable. The thing is, metrics don't capture the previous value of the field, only the current value of the field. What you'd probably have to do is actually have a dummy script in the metric definition, and use a business rule instead to create the metric instances based on your criteria. Let me know if you have that kind of specific need, and I'll try to help out.
Otherwise, try the script linked above, and let me know how it goes.
Hope this helps,
--Dennis R
