The BLP Problem

[Linkmaster]

Hello guys!

I have a simple question: Is there a way to convert png files into blp files and make them work for the world editor?Because i need some wow Icons and all
Wow icons are in png format.

I tried it with http://wowdev.org/wiki/index.php/Wowimage but if i convert them they wont work, Instead of the icon there is a green icon...

Edit: Okay forgot it...Now i dont make the icons for myself i just download it from the icons database... its senseless to make themself ^^