if you step in fractional amounts then you need to use floats, so add a # to your variable name...eg
FOR A# = 130 TO 450 step 0.1
SPRITE 17, 100, int(A#), 17
NEXT A#
although unless you want your game to stop at this point while the sprite falls then you need to forsake loops and use a logical compare to move your sprite so that it will keep moving the object a little each loop...eg
if A<450
inc A
SPRITE 17, 100, A, 17
endif
will move it once per loop until it reaches the bottom.
if you listen you can hear the inter-dimensional zombies calling.....branes, branes......
