We saw the HTC HD2 run Meego, we saw it get an upgrade to Windows Phone 7 and it was capable of running on Android as well. But now the folks over at xda developers have gone one step further by making it possible for HD2 users to dual-boot Android and WP7.
“Why have one when you can have two and choose between them at will” seems to be the motive behind the move and while the process is incredibly complicated, there's something sweet waiting for you at the end. All you need is two SD cards and a very patient mind to go through the instructions in this thread.
As always though, this isn't officially supported so it could be extremely risky. Exercise some caution while going through with it because it might end up bricking your phone.