I am running GSB on steam but I have downloaded the campaign because it looked really cool (and it is).
I have steam on my laptop and my PC with GSB installed on both. Is it possible to install the campaign on my laptop and my PC at the same time legally and technically?
Yes and yes. I have installed and reinstalled GSB countless times, on both my desktop and my laptop, it’s fine as long as you don’t lose your registration key (and cliff is usually kind enough to resend it to the email adress you used to purchase the game if you happen to lose it) and your user name. The campaign isn’t any different.