Can't decide between WP7 and Android?  Thanks to some of the minds at XDA, now you don't have, if you have an HTC HD2.  Due to limitations in both operating systems, WP7 will reside in NAND memory and Android will be booted from an SD card. 

Here's what you will need for the recommended method:

Once you've gathered your materials, go here to get started, or you can find another method here.  Good luck!  Try not to hose your HD2.

Source: Ali Waqas (Thanks for the tip!); via: XDA