Yes definately is, but I think that its only available using Intels Virtualisation, I know that Virtual OC (which is free) definately uses Virtualisation (on most Conroe chips) and so does VMware server, I have installed a 64bit OS on a 32bit host before now, using both software...
Stelly
I think it's actually more difficult to get a 64bit OS on a 64bit host because of driver signing. I haven't managed it yet :/
Was that virtual PC you were referring to, or what is not a typo? If not, can you link me to the software.
EDIT:
Used Virtual PC 2007 and it appears to have worked ok.
You can do it in the lastest version of VMware server
Burnsy