We’ve been seeing Android (and Ubuntu, for that matter) builds running on the HD2 for a few weeks now, and it looks like an early prototype build is now available for download.
Compared to what it takes to alter your OS on Android phones, it actually seems quite simple:
Global instructions: Just extract to Storage Card root directory and run HaRET executable.
Android build with HTC sense (tm)
composed by DarkStone1337