I think you use Gimp, so this technique might not work. It should work the same way as what Xbladez said.
Presuming Gimp has a magic wand tool, (and I think it does because I've heard other people talk about it before) apply these settings. Hopefully they are the same in Gimp. The default Tolerance for Photoshop is 32.
Then select the white bit you want to get rid of and hit delete like you would normally do. If this way is a tad confusing, just ignore it and use Xbladez' way because that's simple, and it works.
