GUI Button Help

I have an image i want to use as a button, and another image i want to use as its down state. Neither of which should be scaled. How would i go about implementing it in the GUI builder.

How does it take the image supplied in the bitmap property of its profile, and use that to make the button. Does it have to follow certain size/spacing guidelines etc... I've looked at the button png in the common folder, but mines got more detail than that button.

Any help would be appreaciated.