Hierarchy selection: picking multiple countries and regions

I have a client who has a strong international focus and who needs to  
let his users specify a set of countries and/or geographical regions  
-- for instance, he'd like them to be able to pick "Central America or  
Mexico" and so come up with the set of all the countries in Central  
America, plus Mexico.  The assumption is that we would structure the  
list of all the countries into a hierarchy of regions (e.g., Africa,  
Caribbean, The Americas) and sometimes sub-regions (e.g., Central  
Africa, East Africa, etc.), and then let the users pick either  
specific countries or regions (thus selecting all the countries within  
the region).

I've been able to disabuse him of the idea of trying to do this with a  
multiple-selection listbox, but now the question is how to do it.   
I've spitballed a few ideas --

	* each region gets a checkbox and a "twisty triangle" that, when  
clicked, opens to reveal the sub-regions and/or countries, each of  
which has its own twisty triangle and/or checkbox.

	* the old Mac "font mover" design: a list of selectable stuff on the  
left side of a display; selecting something enables an "add" button  
that, when clicked, moves the selected things to a second list on the  
right.

but I'm not in love with any of these just yet.  There are obviously  
some tricky issues about data representation in all of this that I'll  
forego for now (e.g., the difference between picking a region vs.  
picking all the components of a region); my current plan is to get the  
interface right and deal with the data structures later.

This is clearly a specific case of a more general problem of picking  
stuff from a hierarchy, but I haven't had much luck in finding  
solutions to similar problems.  Any thoughts or suggestions out there?

Thanks,
Jim

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