KVM doesn'r support ....

How is it then that I've been running 32-bit Linux and 32-bit Windows in KVM running in my 64-bit Fedora 8?

Sadly, I don't think either KVM or Xen matches Virtual PC on Windows yet.

As for running FreeBSD on Xen (I've not tried it on KVM yet), just run this google, it's still a current problem:

http://www.google.com.au/search?num=100&hl=en&safe=active&client=firefox-a&rls=org.mozilla:en-GB:official&hs=EYY&sa=X&oi=spell&resnum=0&ct=result&cd=1&q=%22BTX+Halted%22+xen&spell=1

I've been running Debian and Windows Server, virtualised, on the same hardware that gave me much grief with xen and KVM and most particularly, libvirt. I was hoping the stuff Ubuntu had used until now was going to provide a viable alternative.