As one of the organizers of this event - I'd like to invite and encourage team entries from anywhere (well, on this planet at least). Last year in Reno, we had 4 US teams, one from Canada and one from Taiwan. Team Canada won backed by SGI. Most of the teams used Linux, however one team used MacOSX.
The deadline for entry for SC08 is the end of July - so you have time to get your act together. But start now, because you need 6 undergraduates, a supervisor and a corporate partner (who will supply the system for you). The above url is where you can learn more and/or send email to cluster-challenge@info.supercomputing.org if you have questions. Last year we had vendors looking for teams - so there is the potential for match-making.
Brent