I have G2 and I don't need to have the CD in the PC to run the sim; however after registering it and entering some troubleshooting codes (to get Add-on 1 working) the software reported that it was locked to my PC. I'm not sure what that means. If I had another PC I'm sure I could load it but probably not register it to 2 machines.

I also remember reading that the license is only for 1 machine. Besides I don't think you can run both copies simultaineously because it needs the controller plugged in. At least that's how it works on my G2 USB version.