Cannot install Ubuntu on MBP, using USB stick or DVD

Hey,

I have a MacBook Pro, I've downloaded the latest version of Ubuntu which is compatible with my MBP. I downloaded the file, burned the .iso onto a DVD. I've insalled rEFIt, which works just fine. When I boot the MBP with the alt key pressed, the rEFI menu appears, but the disc image doesn't hopefully you will understand what I mean.

After a few attempts, a new image appeared 'OS Legacy' or something similar, I click on this one and it says it's not available.

I then went through the method of installing Ubuntu onto a USB drive, I converted the .iso to a .img file and mounted it onto the USB drive. Same steps as before, held the alt key when booting and still nothing.

Is there anything that I'm doing wrong?

I hope to hear from you soon, thanks in advace.

-John