Depends on how you are going to use it. If you wanted to add the picture to another image in photoshop, you can select the white space around the image with the wand tool and delete the white. When you copy that layer over another layer, the background will show throught.
When the white has been removed you can save it to a format that supports a tranparency,such as gif or png, that way you can open that image in another program (or add it to a webpage, for example) and the transparency information will be retained.
Let me know if that makes sense to you, if not maybe post what you are trying to achieve and someone can give more specific pointers.