So, I'd say someone was on the ball just waiting for "April Fools!" This appears to be a very well constructed practical joke for April Fools Day.
(I admit this suckered me in. I came back and modified my post after testing and remembering what day it is...)
"As we have just announced over 1 MILLION downloads of Virtual PC 2007 (since its release on February 19, 2007), I have been cleared to post about a hidden feature in VPC 2007. As it is still in a Technical Beta phase, the option to enable support for the installation of Mac OS X is not part of the GUI, but can be enabled at runtime with a command line switch. Although the feature is still experimental, I have been running it at home for the last 2 months, and have had very few stability problems."