I own Heroes of Might and Magic III original,
I own the Collector's Edition with HoMM3 included,
I have downloaded some ugly copies of HoMM3 from the internet,

none of theese run on WIn7 64 bit. Have the same problem described on every forum on internet...

Got my hopes up when someone recomended this site... Paid for gog's version og HoMM3, but still the same problem like the rest of the world have with it...

So... How can I get my money back?

And even more... is it worth buying other games on this site... ?

Money back?... lol.

Have you checked the subforum for the specific game? People might be able to help you there.
http://www.gog.com/en/forum/heroes_of_might_and_magic_series/#1332684105
Also contact support, they might be able to help. Contact support, I suppose. I own quite a few games on here - 50-60 or so, but not the specific game in question - and have not had any issues with getting them to run on Win7 64.

Have you tried right clicking it and enabling some compatibility options? I've played it on Windows 7 64bit and I set it to run in Win 98 compatibility mode & 'always run this program as an administrator' and it runs fine. If that's not enough try disabling desktop composition on that same compatibility page.

Edit: As for is GOG worth buying from again? Absolutely. I have over 100 games bought on here and of those, only 1 doesn't work. They do a good job of releasing oldies and they're pretty good at interacting with the community too and the support forums are also generally good.

What exactly is "the same problem"? You may try the HOMM forum for a solution and maybe GOG support.
Unfortunately you can't get the money back.
Yes, it worth buying other games on this site.

I got a broken sword game it didnt work, got no refund, but the tech support were very friendly and helpful even though ultimately it didnt work, but a retail boxed copy did.

Try the tech support.

I have no issue with the HOMM3 version from GOG it works just fine. I use Win7 x64 Ultimate...

Sorry, all payments are final

So have you tried to look at this also?
http://www.gog.com/en/forum/heroes_of_might_and_magic_series/

EDIT: Wow, 7 posts in 1 minute :D

First thing I can tell you is that it is NOT related to Win7 x64. My retail and GOG versions (my retail version is the German "Purple Hills" version) work fine at my end.

From the Terms of Use: A sale is considered final after 7 days after purchase, or when you make a download attempt.

I just now installed and started the GOG version of HoMM3 on my Win7x64 machine, just to check. It works fine. No compatibility settings, no administrator stuff, it just runs, straight out of the box.

Your problem is not related to your OS. Except maybe if you installed the game in the Program Files folder. That's always a bad idea with old games on Vista/7. So don't do it.

I have all those too, and they run on Win7 64bit. The problem might be something else entirely.

What kind of "does not run" are you talking about?

/edit: actually, I don't have ugly copies of that from the internet, so disregard some of what I said. Also, ninja'd on the second one :p

Maybe you should try installing DirectX :D