Unable to boot via USB

Hey!

I currently bought a Sandisk SSD 240GB to my 15" Macbook pro. Therefore I would like to install Mountain lion on it. (It was brand new when i bought it, so its already empty).

I tried to create a bootable USB unit, by following this tutorial exactly (it succesfully installed): http://www.youtube.com/watch?v=aee0rZXowEA

But whenever i try to boot my mac with the USB plugged in, pressing the option key, I am unable to boot from the USB. As far as I know, i should be able to view and select the disc image in order to install Mountain lion, but I dont have that option. Instead I am only able to connect to the internet, and nothing else.

Even if I boot with my old harddrive (Toshiba 500GB), I dont get the option either to boot via my USB disc image.

Note: My USB device is a Samsung 1TB.

Thanks!