Hmm... The 'big bang' WAS indeed an "explosion" without a centre. Unlike a conventional explosion (which is only related as an illustration that lay-people can easily understand) it wasn't actually an explosion in the usual sense of the word. It was a sudden expansion of all of space.
Try to look at it with an open mind for a second. I'm not entirely sure I'm that great at explaining this sort of thing. Try thinking about it with an open mind and try to envision what it WOULD look like to have an infinite space suddenly expand from a point to the early universe.
Scientists weren't in agreement on whether the universe is infinite or not last time I checked (I'm specializing in lasers and acoustics and astronomy is only a hobby, not something I read all the journals on) but the big bang theory is consistant with both. If the universe were infinite, imagine all that infinite area compressed into a point, and then 'allowed' to expand suddenly. There is no centre as nothing exploded within the universe (even a finite universe would have no observable centre created by the event). I just find it easier to comprehend when I assume an infinite universe as such a space, by definition, can have no centre, and yet an infinite universe has ALWAYS been consistent with the big bang theory.
Of course, nobody knows what caused the big bang, but as the universe is still expanding (and, as this last year has shown, it's actually accelerating) it's difficult to claim that this big bang model has no merit.
Note: this has never claimed to have anything to do with what caused the big bang. Science deals with observations and predictions. When variations in the cosmic background radiation were predicted (according to the big bang theory) many scientists thought it would be the end of the big bang ideas as they hadn't yet found variations. A few years later, they sent a telescope into space sensitive enought to see the variations and it's since been confirmed many times over. Many people (generally Christians) here think God did it, others (*cough* atheists *cough*) don't have a problem with the idea that it happened spontaniously. Neither invalidates the big bang theory which models our universe's timeline, not the creation of our universe.