Tunnel between two IPv6 islands in an IPv4 ocean?

[Rick Thomas <rbthomas55@pobox.com>]

What would be the "Debian way" to set up a tunnel between two routers  
running Debian to connect two IPv6 islands in an otherwise IPv4 ocean?

To be a bit more specific:

There are two groups of us in my University who are experimenting  
with IPv6.  The rest of the University is entirely IPv4.

Each of these groups has gotten themselves a tunneled router  
connection to the IPv6 backbone outside the University, and we can  
communicate using IPv6 by going out to the backbone and back into the  
University via these two tunnels.

But that seems overly cumbersome.  It would be great if we could  
connect the two groups directly with an IPv6 on IPv4 tunnel that  
never leaves the University.  If possible, I'd like to use two Debian  
machines to do this.  Does anybody know how/if it can be done?

Thanks!

Rick