What "Virtualization" are you using now?
Or in the past.
Apple may be developing virtualization software that would allow Windows to easily boot on the MacOS while still having MacOS active. I don't quite understand how this differs from Virtual PC, if at all, except Intel has apparently added (or will add) support for such things in its processors. They claim Apple is working closely with Intel and Microsoft on this. This will apparently be in the next version of OSX code named Leopard.