Hi guys,
1) I was able to install WMP 10 on Windows 7 32 bit, following the instructions posted by Leandrini. At the end, everything worked fine and I had WMP 10 running in Windows 7 32 bit with no issues!
2) I was not able to install WMP 10 on Windows 7 64 bit, following the same instructions. At the end, like user Mew, I was not able to find "installed versions" on the registry, and got the same error message he did.
So, it seems you can install WMP 10 on Windows 7 32 bit, but you can not install WMP 10 on Windows 7 64 bit!
Fortunately, just before trying to change WMP version on my Windows 7 64 bit, I had done a complete partition backup (I use Macrium Reflect to do it). So, when I ended with not WMP at all, I just recovered the partition backup I had made less than an hour before, and at I got my Windows exactly as before changes, and ended with my WMP 12 again.
* Some people ask why we insist on WMP 10 instead of other media players. Well, for me there is a very good reason. I have a hearing loss (in my case, it affects the frequencies above 2 kHz). In 2004 a guy made a customized DSP dll file for me, with performs a very advanced compressive equalization that makes music sound again vivid to my ears. With WMP 10 I could just go to "plugins", "DSP plugins", click in the "add plugin" button, point to the dll location, and get it working. In WMP 11 and 12, Microsoft removed the option of adding a DSP plugin directly from a dll file in the computer. And that specific dll does not work in other players, just in WMP. So in order to be able to having pleasure listen to music with my hearing problem, I think I will change Windows 7 64 bit for Windows 7 32 bit... better to have that Windows 32 bit RAM memory limit (4 GB) than not being able to listen properly to my favorite music!