@RPMiller: There's no real chance of the machine 'failing' as such. The Standard Model of particle physics predicts that there is a Higgs boson. If it finds it, Peter Higgs gets a Nobel along worth the experimentalists that find it. If there is no Higgs found, then the entire Model has been disproved - which would be a major result as it would mean that one of the best tested theories ever constructed would be disproved. Finally it could (and is widely expected to) produce a whole world of new matter that we've never seen before, in which case it is champagne all round and a lot of work for me.
The way it could fail is to not actually produce collisions of the energy required, at the rate we need. That would be an engineering failure and is possible, though, we hope, very unlikely. Nevertheless, the collider is scheduled to run for 10 years at least, so even if it doesn't work as expected when it starts, it should be fixed soon enough in that 10 year window. We'll have to wait and see what first runs this summer produce to know how well the machinery is working. Something this large, complex and unwieldy is guarranteed to have teething trouble when they flick the on switch. The question is how serious the problems are and whether they can be fixed before the first physics run next spring (it turns off during the winter because electricity is too expensive and the experimentalists need downtime to tinker).
@Neonknight - There are many theories with extra dimensions, all of which differ on their nature. Every one of them has a good reason why we haven't seen them yet. These generally fall into one of two categories - either atoms can't move in them, but more exotic matter such as gravitons (a hypothetical particle that transmits gravity) does. Or they are very small and circular. By circular I mean that if you travel far enough in that dimension you get back to where you started - like in the Meteors! or Maelstrom games where if you fly off the right of the screen you come back on the left. In the case of these dimensions, the width of the screen is of an atomic scale, so you would never notice the process of moving across it and coming back to where you started.
There are theories with other universes that are separated from us because of the way space-time might split in quantum mechanics (ala quantum leap and parallel universes) but that is a different use of the word 'dimension'.