Can anyone tell me what i'm doing wrong here?

It's that little bit of white on the images im importing that's causing me problems. You can see on the right, surrounded by red, what i'm importing. I've noticed some other skins using the images with the white on but it seems to not be a problem like it is on mine. They are bmp's. Im not setting any transparency. Is there something i'm missing to make the white bits not show?
I noticed the Solarion skin uses a similar image but the white does not cover the tabs like this when applied. I hope someone can help me.