Thanks for answering.
The other question is can I install the game on 2 or more pc and play them at the same time?]
If you bought from GOG.com the answer is yes to both. If you bought from Steam you can install as many times as you want but you can only have your account online on one machine at a time (offline mode should work though). Retail and other stores have SecuROM with 5 machine activation limit.