Q: Is it possible to run 64-bit OS, such as Vista 64-bit, on a 32-bit CPU? I don't care how slowly it runs, if it runs at all.

A: No, it would not be possible. 64-bit OS would issue 64-bit commands to the CPU, and 32-bit CPU would not understand those commands at all, and will crash (for the geeks, it would be "invalid opcode" error).

I suppose you *could* write a virtual machine that emulates a 64-bit CPU, and run the OS within that, but then you have to intercept very single call an OS can make... pass-thru if necessary... Why? When 64-bit CPUs are readily available?