None of the Slingboxes have the ability to be used as a Windows Media Center Extender. You may want to consider contacting the author of that article, Stephen Lilley. It's possible that it was a typo or he has a secret that nobody else knows.
on the box of a slingbox pro-hd it says quote video and audio sources (any of the following) unquote
the 7th item down states Windows Media Center
a person reading this in a store would tend to believe that a $300 item that has a TV tuner would be able to connect to a windows media center since a $100 pci TV tuner card can