I programmed a MAC address generator quite a while ago and I've lost the source code. While I programmed it, I distinctly remember that there were certain rules that needed to be followed to generate a MAC address, but I can't find them.
I think it was something like the second character needs to be 0 or something along those lines.
The first bit needs to be zero for a unicast address. For a multicast address, that bit must be 1.