Dear Mr. B.
I am a high school (formerly middle school) math teacher and built a math/writing unit around the abacus for my 8th graders. The tech teacher in the building worked with kids to cut parts for a home-made abacus for each student. We used small dowel rods, wooden wheels (for cars) as the beads, and small nails (brads) to fasten the frame together.
The scenario was that students worked for a marketing firm and had to develop a brochure to describe how to build an abacus from the "kit," and then how to use it to add. It was then to be marketed as a "summer travel toy."
The first day was a bit noisy, as each student built their own abacus, but the results were good and students seemed to enjoy the project.
I can provide you with more information if you're interested.
I've really been enjoying your site ... I discovered it through taking a "Build your own website" course, and I'm working on using grant money to get a computer projection system for my classroom. I'd love to share your goodies with my freshmen (that's all I teach this year).
Several years ago I published an article in Mathematics Teaching in the Middle School (May '97) on the algebra behind a card trick. You may enjoy taking a look at that ... it'seems to fit in with the Math-attitude of your site!
Thanks so much for a great gift to mathematics, teachers, and students!