well i was having trouble with fallout 1doing rainbow pixels and so i enabled 256 colors and the 640x480 screen resolution and it began to work fine but when i did the same thing for fallout 2 the screen goes really big and it says "error: fallout is running in compatitibility mode: and will not go to the game but if i turn off those two things it works but has rainbow pixels and i dont know what to do. can someone help me

Did you grab the latest patch for Fallout 2? http://gamesas.com/support/support.php?id=120

If that doesn't work:

Download sfall from http://sourceforge.net/projects/sfall/
Unzip it to your Fallout 2 folder
Open the ddraw.ini file in Notepad
Look for the Graphics section
Change the Mode 0 to 4

That compatibility mode error is from sfall, not fallout, so it's already installed. If you installed it yourself, or installed killap's patch, then rtfm to find out how to fix the colours problem. Otherwise see this thread.