Steam is the best thing to happen to non-console, non-mobile gaming in a couple of decades. If the resolution of the host display is set in-game to the same as the client, that's that much less work the client has to do. It sounds like as much of the work, including graphical work, as possible should be done on the host. Click on Add a game, and then select Add a Non-Steam game option. Remember, the client can be a low-performance device, so long as it can sufficiently play the stream, as it doesn't handle rendering the game's graphics. Next, open the Steam software, and go to the Library. There are three methods you can use to play Windows game on a Mac: WINE, Boot Camp, and virtualization. While it would be feasible to do this on a headless server with a beefy processor and minimal graphical power, you're almost certainly going to get better results if a decent enough GPU is used on the host. Ideally, the hosting machine would need to be powerful enough to play the game and to encode the stream simultaneously. Name your drive something appropriate and click Next one more time. Select your preferred version of Wine, then hit Next again. Click Next in the PlayOnMac Wizard and then select 64 bits windows installation before clicking Next again.

Does the hosting machine need powerful graphics or would a headless Xeon PC server work well? I ask as I am looking at getting one anyway to host opensim and that only being a database doesn't require much in the way of a GPU the graphics being handled by the client viewer. On the main PlayOnMac window, select configure, then click New on the bottom right of your screen.

Can i play windows games on mac steam