You spelt video_depth wrong.You have to use the BMAP pointer when creating a BMAP and you have to put the name in "" instead of <>. You can just set the panel's visibility using the flags=visible;. Also dont put a ; after u define a panel or function.

This should work>>>

//////////////////////////////////////
VAR video_mode=8;
VAR video_depth=16;

BMAP schwarz_bmap="Bild.pcx";
//////////////////////////////////////
panel bild_pan
{
pos_x=0;
pos_y=0;
bmap=schwarz_bmap;
flags=visible;
}
//////////////////////////////////////
FUNCTION main()
{
load_level("tut_level.wmb");
wait(2);
}