I've been thinking of getting a dual Opteron box lately and I found this on linuxjournal.com:
Unlike Intel's Itanium, the Opteron can run 32-bit x86 code without emulation; it runs 32-bit x86 code at least as fast as an Athlon does at the same clock speed.
So does this mean I can run regular old i386 debian on an Opteron box?