Where is 'fpsdl.bmp' located in the directory structure? According to your code the bitmap must be located in the same directory as the executable itself (or the root directory). So if it is located in a subdirectory then you should include that as well:

[pascal]
picture := SDL_LoadBMP('subdir/fpsdl.bmp');
[/pascal]

SDL_LoadBMP shouldn't return nil if the bitmap is found where told. It's worth taking a look at your directory structure and make sure where the bitmap is located.