If like many long-time Windows Phone users you have an HTC HD2 lying around, you could do a lot worse than installing Windows Phone 7.8 on it.
JuicyBoose has posted a detailed step by step tutorial which would guide even a novice through the procedure of installing the OS, but one should be warned that while it does a good job of showing the way, it does not provide much help if something should go wrong.
On the other hand, with the HTC HD2 how more than 3 years old, what is there really to lose?
See the video and the associated thread at YouTube here.
Thanks CODE for the tip.