We never did try Linux on that particular machine, but tonight Nick, James and I gave it a shot at the UCC. After some wrangling with various kernel versions and booting methods, we came to this conclusion:
In February 2008, Linux does not work on the SunFire V480.
We only used Debian kernels, but tried CD booting 2.6.18 and 2.6.22, both of which failed shortly after loading the kernel with "Illegal instruction" error messages. Netbooting was unfruitful, simply freezing the system. (It's possible, but unlikely, that the netboot image switched to serial console for output.)
If you own a V480, stick with Solaris. You'll be much happier, and you won't have to employ a kernel developer to get it working.