Thanks, that was it. I wonder why it isn't in the 'guides'. I couldn't find it in the online mac help shortcuts either.
When I tried it though, my mouse wouldn't work, although I did plug it in after I got to the screen where you choose the startup disk. The keyboard arrows weren't doing anything either. My start up newly created disk also didn't show up.
After a couple of minutes the new startup disk did show up and the arrow keys seemed to work. I say 'seemed' because there appeared to be a one minute delay before the startup disk changed.
When it did finally select the new startup disk it worked fine. Is this sort of delay normal at this screen? Also what does the circular arrow mean and which keyboard button controls it.
EDIT: I just added it to the 'Mac Guides' System Startup. That was exciting.