Thanks Tim, Andy, Gilles and Lubomir.  I bought the Marble Mouse and
it works after a fassion.  The large left and right buttons work and
the ball steers the pointer around the display.  I would like one of
the small buttons to work as though it were the middle button on a
three-button mouse.  This may be the default (it works for me in
Oberon).  Perhaps it doesn't work for me on NetBSD because of a
config file tweak that I did (and sadly failed to document) way back
when I began using an optical mouse with a scroll wheel.

In an ideal world, the remaining small mouse button could be held
down while the I moved the ball to simulate a scroll wheel (sending
the scroll events to X without moving the pointer).  I imagine this is
possible, but I lack the programming skills required to make it
happen.  Any volunteers?  :-)

- Andy Ball