@Les I am sorry i forgot to respond to your note.
At the moment the boards list is read from two places. The arduino ide hardware folder and, if it exists, the sketchbook\hardware folder (as documented for the standard arduino ide)
My understanding is that when you install teensy it modifies the arduino exe and version and I guess it uses a different folder to find the boards.txt. Otherwise you would see them in vm.
I wrote to the teensy people a few months ago to ask about their config and i received a great reply back but have not yet had a chance to review the outlined procedures.
I don't expect it to be difficult but generally vm needs a better way to support different platforms.
The most recent vm version is a step towards multi platform because the compiler process now uses a single xml definition file that describes the work it needs to perform and for which platform. There is still work to be done but development is moving along at a steady pace.
The idea being that you get to use teensy boards, arduino 0023 boards, arduino 1.0 boards, maple boards, arm boards and others.
If I get a chance I will review the email from teensy but if you have any ideas of suggestions please speak up.
I hope this gives some hope for the not to distant future