Unit/Building Button Spacing, Black Button, How Is It Done?

I would like to create a black button to insert in my unit/building build menu's to act as a spacer to make the menu's look more asthetic. What program would I use to convert X filetype into .blp?

Image Extracter II is a good one.

-Insaniteus-

How would I impliment it into the map so its battle.net playable?

Nevermind. Thanks Instantanious. That program, in conjunction with WinMPQ, MPQ2K, and two tutorials in the tutorials section worked great!