|BeOS for Intel:
The definitive answers to this question are on the BeOS Ready Systems list:
To give a few more details, the BeOS for Intel Architecture supports the Pentium, Pentium Pro, Pentium II, and Pentium II Xeon in single and multiprocessor systems (and, of course, we do plan to expand hardware support in many areas in future releases).
Compatibility is more dependent on the motherboard design (or more accurately, the core chip set) than the processor itself, so not all systems with the above processors will necessarily work.
This also means that the BeOS will run on some systems based on clone processors, such as the AMD K6 and K6-2, and the Cyrix 686mx (though other Cyrix processors have proven problematic).