There shouldn't be a problem with win 7 64-bit, since most of the games either use DosBox or ScummVM (already implemented in the installer).
Besides, the GOG team test all games on all win configurations - XP/Vista and now win 7

As for GK1 I can confirm it plays beatifully on Win7 Pro 64-bit.
The thing about GOG.com is, that you get addicted to games from them, because it's so darn easy and a trip down memory lane
