can I download the necessary data if I can provide my serial somewhere

Yep! Just grab Stardock Central from the downloads page here. Once installed, log into it with your forum account, and go to Tools menu->Register Products. Pick the Games section, find GC2 in the dropdown list, and enter your email and serial. GC2 should then appear under the 'Purchased Products' heading in the games section of the main screen; just select it and click Install to get it (Make sure to hit the [+] next to it and grab the subcomponents as well).