Transparent textures in cycles

Hi!
I’ve modelled a bicycle wheel and now I want to have stickers on it. My idea is to have a (colored) PNG with transparency, and where there is transparency i want the material of the rim (matte aluminum) to show.

Can this be done in cycles?

(All I’ve found so far is how to make certain colors of a JPEG transparent. I guess that would work to if my texture didn’t desaturate and if I could make those transparent parts into aluminum instead and if that didn’t give shadows from the transparent parts…)

Tutorial on adding decals in cycles http://www.andreucabre.com/2012/02/multiple-uvs-and-decals-in-cycles.html
Use a texture format that can have an alpha channel like .png instead of .jpg

Thank you! That is exactly what I am looking for. Unfortunately I do not understand a thing of what Andreu is doing. I cannot see how he sets up the rest of the nodes and all i can achieve is a black picture in the image editor when I load the PNG - which makes my whole model black when i render.