I have 2 free and 1 purchased game that I have tried to download. Have updated my drivers, checked for all other udates, uninstalled, reinstalled, restarted, and if they weren't downloads I would have thrown them out the window in frustration!!! My Big Fish games play with no problems, same with Popcap and any other sites I have dowloaded from...Just Amazon giving me problems, comes up with a "game has stopped working. A problem caused the program to stop working correctly. Windows will close the program and notify you if a solution is available."
I too downloaded the free game, Big Kahuna Reef, about 1 week ago. I have Vista and also have antivirus protection. I haven't had any problem. I too have Big Fish games, haven't tried Popcap but will. The Big Kahuna Reef is the only one I have downloaded from Amazon. Hope you find a solution.