There is a sticky in this very forum that discusses how to do this:
[Guide] Android on your HD2 from start to finish
The whole process looks daunting but I did it on a buddy's HD2 (I have an Evo myself) and it was really pretty simple once you get the hang of it. Really, you just need a few things:
- install a "hard" SPL such as 2.08 HSPL
- install a new radio version that will allow you to use all 576MB of RAM instead of being limited to 512 (such as version 184.108.40.206)
- install MAGLDR 1.13
- flash your desired Android ROM
- google your APN settings for your carrier and country and plug them in (this will get your 2G/3G data working for when you are not connected to wifi)
The only part that you really need to be careful with is the radio version that you flash. Flashing a radio not designed for this phone can brick it. Otherwise, if you have a hard SPL installed then even if a ROM doesn't work, the phone will always fall back into the bootloader so that another ROM can be flashed to get things back up and running again. A hard SPL also allows you to flash unsigned ROMs. Of course, if you flash the wrong radio then your SPL version won't matter because the phone is bricked.
There are plenty of tutorials out on google, youtube, and even in that thread above. I flashed the "prj clean Desire" ROM to my friend's phone (it's a Sense-based ROM) and it works beautifully. The only thing that doesn't work is 720p video recording.