I'm not sure what program you use. There are a couple of different ways to do it. If you have the option to change the layer style you can choose either Darken or Multiply. If you don't have a layer style option you can select the white area with your magic wand and then delete. If it leaves a bit of white around the edges you can zoom in and begin erasing by hand.

It looks great!
Dec 7, 2007