Xeons are x86 processors (like Athlon, P4, etc) manufactured by Intel. Given they are x86 architecture, they can run any OS that an Athlon, P4, etc. will. They are similar to the P4 except for a couple of differences:
They are designed with multiprocessor (SMP) applications in mind
They can have larger on-die caches than P4's
There are other more subtle differences but these are the main ones. Given this, they are produced for workstation/server markets and are not targetted towards home users (that's for the P4).
Hope that helps,
Andy