Hello,
Still trying to get the hang of GOG. I have downloaded the AC planet pack and there is an icon for Alien Crossfire on my desktop but how do I get Crossfire to play? When I click Play it starts AC and offers no other choice.

Thank you

There should be two executables in your installation folder; terran.exe opens vanilla SMAC, and terranx.exe allows you to play Alien Crossfire.

If you prefer to use Galaxy, instead of "Play", click on the options button next to it (called "More" in older versions of Galaxy), then on the displayed menu click "Additional executables" and select the expansion (Galaxy, by default, launches the vanilla game).

Thanks for the help but pressing More and the Crossfire nothing happens (same for the Editor} and I cannon find terranx.exe: where is the installation folder. Dumb questions I know. Thanks again

For me the installation folder is D:\GOG games\Sid Meier's Alpha Centauri (first attached screenshot). But this can be changed on both offline installers and Galaxy so yours could be slightly different.

If Galaxy is giving you trouble, you can go to your account ( https://www.gog.com/account ) and download the offline installer directly (second attached screenshot).