select certain material in compositing

I am using cycles and I got a multi-material model. I want to select that certain material of my model and blur it or something.

if I’m right, color pass something selects a certain color, but what if it is an image?

and oh, I’m a beginner with compositing.

Give the material a pass index and in the render layers enable Material Index. You can then isolate that material in the composite.
This tutorial includes such a thing http://www.blenderguru.com/videos/create-a-spaceship-part-2-of-2

oww… thanks!