<p>Can I run a 64-bit VMware image on a 32-bit machine?</p>

<p>I've googled this, but there doesn't seem to be a conclusive answer.</p>

<p>I know that it would have to be completely emulated and would run like a dog - but slow performance isn't necessarily an issue as I'm just interested in testing some of my background services code on 64-bit platforms.</p>

I honestly doubt it, for a number of reasons, but the most important one is that there are some instructions that are allowed in 32-bit mode, but not in 64-bit mode.  Specifically, the REX prefix that is used to encode some instructions and registers in 64-bit mode is a byte of the form 0x4f:0x40, but in 32 bit mode the same byte is either INC or DEC with a fixed operand.
Because of this, any 64-bit instruction that is prefixed by REX will be interpreted as either INC or DEC, and won't give the VMM the chance to emulate the 64-bit instruction (for instance by signaling an undefined opcode exception).
The only way it might be done is to use a trap exception to return to the VMM after each and every instruction so that it can see if it needs special 64-bit handling.  I simply can't see that happening.