You'd have to do something like
Code:
glViewport(0, 0, w/2, h);
.
.
.//projection and rendering settings for first half of window
glViewport(w/2, 0, w, h);
.
.
.//projection and rendering settings for second half.
You're essentially telling OpenGL to draw two viewports in one window, each taking half of the screen's width. You'd have to give each one a projection setting and rendering settings. I'm not sure if you can connect one viewport with another, i.e. have one viewport project one angle of a scene while the other projects another.