BJ, not sure what the problem is...

Are you using the "define brush" option in the EDIT menu? Or are you clicking on the inverted arrow in the Brush Palette and selecting "New Brush"?

With the "Define Brush" method, you need to make sure the area around the shape/brush is transparent, otherwise you'll have white behind the brush shape.

method 1:
Use the pen tool or paint brush and create a shape you want to make into a brush. Make sure it's black (you need black for it to be opaque)
Select the shape (make sure the background is turned off)
Choose DEFINE BRUSH from the EDIT menu
Name your new brush
If you don't already have EXPANDED VIEW selected in the brush palette select it. This gives you the presets for the brush. Here you can set the Shape Dynamics, Texture, Color Dynamics...

method 2: Choose NEW BRUSH from the inverted arrow in the Brush Palette. This creates a duplicate of your last selected or active brush. Change your preset settings to reflect your desired effects. Make sure you rename this brush.

more later...
:)
retrocity