Redhat works like a dream on sparcs. You have to to get the version especially made for sparc though. You can hook it up to the windows PCs by running samba. It is not that hard
THere are many distribution of linuxes out there made for sparc, such as debian, slackware, mandrake..etc
Also, sparc opens doors to operating systems like solaris, netbsd, openbsd. Those are harder to use systems. If you get into any of those OSes, you'll start learning a lot about unix. Also, if you run netbsd/openbsd, freebsd's port "should" therotically work with the computer. This opens door to many many software packages
Also, these systems are supposed to be set-and-forget, they're very realiable. Therefore, if you want to run a dedicated webserver, ftp server... This computer will be great for all those things.
Also, you get to learn a lot about the SUN archtecture. Knowledge is power
Sparks