Well, I thought I should say something, seeing as this is the only topic here about the Hagstrom thing. First off, when I ordered mine, I had to put "KE18-XTAT-PS2" in the extra info/special orders box when I paid for it.
Second of all, I can't vouch for the Soarer/Teensy method (It's my next project with a terminal F), but the Hagstrom (I'm using it right now) is very touchy. Hitting any of the lock keys has a tendency to muck up things, I get a lot of random "\"s when I'm typing, and the whole thing has a tendency to completely drop out at random times...That and sometimes keys will just not work (especially the space bar).
Add on the fact that there's a lot of wire management to deal with (the XT's cord, an AT to PS/2 adaptor, and a male PS/2 going from the Hagstrom to the PC), and it may be more trouble than it's worth to some.
To me though, it's worth it to be able to use a Model F full time, at least until I get the Teensy method up and running (this will be try 2 on a terminal F, first one had a bad controller I think). Love the feel and the sound!