Okay, so I boot up Dark Forces 2, and it doesn't entirely fit on my screen, part of it is cut off. How do I fix this or change the resolution or whatever I need to do so that the full game is on my screen?

In the Display Setup, set the view size to one step below Max. Max is the same size, but disables the HUD.

Sometimes the cut scenes only play in a corner of the screen or can be cutoff, but the actual gameplay fits the screen.