Thanks for the help, but I'm trying it now and still can't get it to work right.
The file I have is 3840x1080, and I'm trying to play it on a Samsung PN50c8000 (Plasma 3D TV). Using the Stereoscopic player, I set the Layout to "Side by Side, Right Image First", and the Viewing method to the same.
That seems to work, except the video is not full screen - it has huge black bars above and below. My guess is that since my display is 1920x1080, it is trying to scale the 3840 down to 1920 even though it doesn't need to since the TV is combining them automatically.
How can I turn that off, so that it plays full screen? I tried using the Full Screen Unscaled option, but then it really did make it too big for my screen, and it looked really weird.