I know we are not supposed to do it, but Vmware is doing it in the new versions of the emulator. I am not sure how it does it but I have a virtual XP 64 machine running at the same speed as the host XP 32 and they ask for x64 processors to do it so I guess they are running x64 processes natively. However switching to 64 mode from inside a 32 bits app sounds like the perfect way of fucking up Windows XP. Does anyone have any information on this?