@celine is away from the office on Sunday, but you really don't need an answer from her.
Each user is allowed to install the software on two different computers. One can be a windows pc and the other can be a macbook.
Just download the installation files to the macbook, and when the install screen shows up, in stead of clicking on the big red install button, click on the tiny grey words directly below that big friendly button that read 'already a member, click here' and then do a log in with the username and password that you already have.