Making HD2 run under Windows 7 64bit and above

Alright, so this bugged me a lot. I have bought a new PC last December, copied all my favourite games to it and wanted to give HD2 a few rounds. Except the game didn't want to cooperate. I have tried many things, but I didn't want to give up yet, so today I have spent a few (?) hours to reinstall the game from scratch to a virtualised Windows XP to see where the problem lies.
Please read this only, if you had your game already installed, you wanted to copy the installed game to a new OS and you failed making it run on your recently installed Windows 7 64bit and above. Don't do any changes if your game works!

Long story short: If you wish to run the game under Windows 7 64bit, or Windows 8 64 bit and the game pops up with the message of
Don't panic. Not like I did. Or give up.
What to do then?

So since Windows XP Microsoft has changed the path to some of their applications by allowing also 32bit support under 64bit. Doing so they had to also change the structure of the registry thus separating many of the settings. Normally under Windows XP installed applications were automatically pushed to HKEY_LOCAL_MACHINE. This then caused lot of issues. In Windows 7 32 bit the 'default' path has become HKEY_CURRENT_USER. In Windows 7 64bit, to allow better 32 bit support, settings had to be separated from the both paths, thus by pushing them to a new subdirectory: HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\ (same goes for HKEY_CURRENT_USER, but not for HD2)

This is how the most important registry entries look like if you use the game in Windows 7 64bit:
This is all you need. Nothing more. Save the entry as hd2.reg, apply to your registry, and you are done. Of course path settings and key must be set accordingly.