The 'Next' button obviously goes at the far right, as it's leading forward. You don't want the cancel button right next to "Next" as there will be too much risk that it's pressed accidentally, so that means 1 is "Cancel", leaving 2 to be "Back".
I would have to agree as well, this seems the best and most logical way. If the window is going to be full screen then the buttons are the right size, if it would be windowed (small screen in the middle) then i would enlarge the buttons a tab bit.