Hrm ... I see your point. This bears further investigation!
It think we will find it is more along the "You can if you want, but why?". Unless you are testing application compatibility.
I think it is also worth noting that the VM copies your hardware not your OS. At least with Parallels, they have their own drivers (I think VM Ware is the same, which is what makes appliances possible.) that serve as a wrapper to the host OS. It makes it less hardware specific. When you boot the VM you will see a generic clone of your hardware, so if your CPU supports 64 bit... I don't see why the VM couldn't.
Seems my suspicion was correct:
Ken Schaefer wrote:
Absolutely (as long as it's x64, not ia64). This topic came up at work, and there seemed to be a fair bit of confusion over what's possible and what's not. Using VMWare Server (or a Workstation version that supports 64bit guests) you can run a x64 Guest OS even though the host OS is still 32 bit. Unfortunately, neither Virtual PC nor Virtual Server 2005 R2 supports 64bit guests. (source)
Also see: http://justindevine.wordpress.com/2008/ ... bit-hosts/
What is required is a change in the BIOS setting on your machine. It turns out that while this Intel chipset supports Virtualization Technology(VT) it is turned off by default from most PC/Laptop manufacturers (mine is a Dell and sure enough it was off) . I changed the setting and bingo 64-bit deliciousness!