[UPDATED 12 Feb 2011]
Here's a stab at a definition of determinism (D), and a subsequent takedown:
D is the claim that all states of affairs (SOA) at any time t+ in a closed system (S•c) are necessarily the result of a prior SOA at time t. No SOA at t+ can fail to result from the SOA at t. There is not––and, on D, cannot be––any causal 'slack' between any SOA and the initial SOA of the universe as a whole (S|U). If D means that 1) all effects 2) necessarily follow from antecedent follow from antecedent SOA (SOA(t)) 3) in S•c, the either nothing accounts for for the initial conditions of S|U and D is false (cf. 1) & 2)), or S|U is not a closed system and again D is false (cf. 3)). Therefore, D is false.
Now, if the claim is that the SOA for S|U is simply 'autonomous', in need of no prior causal determination, then D is false at least for S|U. S|U may "simply be from all time", but, if D is consistent, what determines this is the case? Once we grant that at some kind of SOA can possess causal powers not wholly determined by some antecedent SOA, then we can only ask how far D applies to all SOA's, not claim that it in fact does apply universally. Only if we grant that there is a cause for S|U which is not determined by anything, and is thus radically free, can we account for S|U as a S•c.
This does not mean D is false per se, only that it is possibly true only if theism is true. Without a Creator, nothing can account for the SOA in S|U, which means at least one SOA violates D. Then again, if something can antecedently account for the SOA of S|U, then S|U is open to a causal power exempt from the constraints of that very SOA, in which case, again, D is false.