John-
If you want to make a version of this using a metal rack, you could use multiple sections of belt clamp - such as these extrusions:
http://www.brecoflex.com/index.php?C...ID=3&SMENID=14
However, I think that the stiffness is more defined by the section of belt that is not engaged with the rack than what the rack is made from.
Plus, I have seen this device in person, and it is very cool watching it zip at insane speeds back and forth.

Keith