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Ok;
For the sake of keeping this discussion focussed, I will admit some errors (due to dodgy sources of data - I've rechecked my sources following renormalised's, Sjastro's and Alex's responses - thanks for keeping me on track, guys).
However, if there was originally a point, a singularity of infinite density, mass, etc, etc, which I think is the main message of the BB, then I think by definition, this is the point of origin (and hence there is a trajectory from thereon).
Not trusting myself on this I just checked one of my favourite books (although, probably just as dodgy as my DVD sources - Brian Greene's 'Fabric of the Cosmos'). He states that one alternative possibility of the BB "is that if the universe is spatially infinite, there was already an infinite spatial expanse at the moment of the big bang. At this moment the energy density soared, large temperatures (etc) ... but these extreme conditions existed everywhere, not just at one point ... instead the BB eruption took place everywhere on the infinite spatial expanse. After the bang, space swelled but its overall size didn't increase since something already infinite can't get any bigger. What did increase are the separations between objects like galaxies (once they formed)."
So, from this perspective (which seems to be an alternative spin on the traditional BB), the term 'trajectory' would have no meaning since there is no single point of origin - my problem seems to disappear (as per renormalised's comments).
It seems that my original question, perhaps, was born from my naivity of understanding of the rubbery state of the BB Theory (already known by Alex). It seems that its not as clear-cut as I thought - ie: that it didn't necessarily all start from a single point.
Which is OK. I can live with a "we're not really sure" answer. Actually, that's quite cool - and an honest answer.
Cheers
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