Is your bmp file in the same folder/directory as your .dba file?
you have to make sure that it is in the same folder.
also you dont have to use the get image command just use this:
make matrix 1,7000,7000,50,50
randomize matrix 1,50
load image "floor.bmp",1
prepare matrix texture 1,1,1,1
this will texture the entire matrix the same image though.
But that always works for me!
besides if you want to make a cool level dont use matrixes, use DeleD! its a really good level creation program.
and email me about Milkshape 3D! trust me you will not be disapointed!

later!
-Captain-

Cheers,
Capt. America