At least with Live, people who owned Macs had 2 choices:
1. Play Live: Macintosh Edition. (Yes, a completely separate server exists for Mac players. Last I heard, it is completely dead.)
2. Emulate a Windows environment on your Mac in order to play. (By whatever method you need to do that.) <I, however, am a Windows user and don't know of the specifics for any version of this method.>
For SoD, your only choice will be number 2. However, in all instances, this will require you to have a copy of Windows running on your Mac. (Thus, you will have to have a Windows license.)