Hi,
I found this article on dual boot with Ubuntu and OS X http://www.lifehacker.com.au/2012/08/how-to-dual-boot-linux-on-your-mac/
but my problem is that my CD player is broken, and the article (and others) say that you have to burn Linux on a CD in order to install it. Does anyone know for sure that the same can be done with a USB stick? Or the computer won't see the stick on start-up?

For anyone interested, it's quite some time now that I've solved this problem by combining the tutorial I've pasted in the previous post with this https://help.ubuntu.com/community/How%20to%20install%20Ubuntu%20on%20MacBook%20using%20USB%20Stick

I've replaced the CD part of the first tutorial with the second and it worked fine. Well, when on Ubuntu the fans work a bit too much, but this's got nothing to do with CD player..