These schoolkids built their own for studying rollercoasters, and they have a special vest that holds the unit! Maybe you could do the same with the Mac. Seriously, it may seem off-the-wall but if downloadable data is essential for you, maybe it's worth considering.
http://homepage.mac.com/cbakken/pga/electronic/
I'm sure you could fire the interest of some geek out there to write the program for you (it'd probably take a couple of hours), and then find a friend with a Mac and away you go.
UPDATE: Found this on the web:
http://handhelddesign.com/q/products...rometer_3.html
It's a tiny little card that slots into any Pocket PC, and all the analysis software can be downloaded from their website. Looks like exactly what you're after?
Good luck with it. What are you going to use it for, btw? Aerobatics training?