HI, i know that this question probably has been answered a long time ago but i bought GSB through steam but bought the swarm exp through this website so i can help an indie reap more of the rewards of his labor but i’m not sure where to send the install and i keep getting an error after the install. This will also help with getting the 1.38 patch since steam is slow to update. Any help would be appreciated. And sorry for sounding like noob.
Steam stores GSB inside “C:\Program Files (x86)\Steam\steamapps\common\gratuitous space battles” for me (you might have to change the drive letter, and take off the (x86) if you’re on a 32-bit machine).
This is where you would install patches, and likely where you would install the expansion.
64-bit machine sir 
awesome fellas, (assuming your guys) that helped a ton. I was able to get the 1.38 patch as well. I was going 1 folder too many and that was screwing me up. Once again thanks for the help.
I had the same problem with my install. Make sure to click on the “common” folder not the space battles folder. Fixxed it right up. Thanks.