USE_TRIPLE_BUFFER: this has to do with the way the game will draw the graphics. It reduces tears, artifacts, and flickering of graphics. It also requires more video RAM though so it is disabled on slower machines.
SUBTITLES: Toggles subtitles on and off during the intro cutscenes.

These all have to do with taking screenshots. Press PrintScreen while ingame to take a screen shot. All screenshots are .tga format which can be opened in Photoshop and a few other programs too.
TGA_CAPTURE_WIDTH:1024
TGA_CAPTURE_ASPECT:1.333333
TGA_CAPTURE_INPUT_SCALE:1
TGA_CAPTURE_RESERVE_SPACE:FALSE