can't figure out how to make sprites have "invisible" border

Sorry for such a newb question, but I'm having trouble getting my art creations to show up properly in Torque Game Builder. I can use the "fish art" and other given resources just fine. However, when I try to edit one of these pictures in paintbrush, then save it, when i try to use the picture in TGB again it will have a solid color border of either white or black around the sprite image. Also, if I create a brand new picture in paintbrush, say a starfish (no touching the background while drawing it), the same happens if I try to put my pic in TGB (solid white border.) I guess my question is: How do you create art so that the background of the object is transparent? Is paintbrush incapable of this task? If so , what program (preferably free or cheap) can I use to do this editing? Thanks to all who try to help.