Find the "S3DClient.cfg" file into the game's folder and open it with your notepad. You can see the next lines:
ResWidth=1024
ResHeight=768
WindowResWidth=1024
WindowResHeight=768
RenderLevel=3
AALevel=3
Fullscreen=1
PostRELevel=0
ShadowLevel=0
SoundLevel=100
MusicLevel=100
ResWidth and ResHeight are for the full screen resolution, WindowResWidth and WindowsResHeight are for the windowed resolution, if you want another resolution, change the correct lines.
RenderLevel is the quality of render mode, if the game runs slow on your computer, try to change the value to 1. Warning: Never change the value to 0 or the game will run very slow.
AALevel is the AA filter quality, if the game runs slow on your computer, try to change it to 2, 1 or 0.
Fullscreen is to select the full screen mode, put 0 if you want to play in windows mode.
PostRELevel is the level of post processing, put 1 if you want to disable the post processing effects.
SoundLevel and MusicLevel are to change the sound and music volumes, the values can be from 0 to 100.
