Some later re-releases of the fallout games include unofficial third party mods. (Without permission or acknowledgement, I should add. They've also ignored requests to remove them.
) sfall can be one of the buggier ones, if you don't know what's doing. The easiest answer to your problem is to get rid of it. Find the folder to which you installed fallout 2, and there will be a pair of files there called 'ddraw.dll' and 'ddraw.ini'. Either delete them, or move them outside of the fallout folder if you might want to put them back later.
Alternatively, the version of sfall that gamesas have been bundling is horribly out of date. You might find that a more recent version will work. There's a thread on NMA about it here.