Based on what I think you meant:
Basically when you start holding down mouse, make 2 variables of where mouseX and Y is. When you stop holding down mouse button make 2 variables of where mouseX and Y is.
You now have enough coordinates to make a box. When mouse button is released make a loop for each side of the box, the length of the loop is based on the distance between each point of the box (then divide by 32 cause of your sprite size). Then create the sprite at the index of the loop.
<img src="http://dl.dropbox.com/u/1024727/caps/selectbox.JPG" border="0">
CAP example
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