How I can buy Two Liscence? Do I use commercial?

Hi, I'm interestred on buy Action! but i have some questions. 1. i have two computer, can I install on the two with one liscenced? 2. What is the diferrence betwen Mirillis Store Version and Steam Version? OS: Windows 7 and 8.1 Video Card: NVIDIA Quadro NVS 160M and i dont know! Memory: 4 AND 8 Moni...