If you're mentioning the Heisenberg Uncertainty Principle, you're missing the point. No-one's going to go out and build Laplace's Demon (It certainly wouldn't fit in the garage :). If you were to build one, you'd be tripped up by more fundamental problems, like how to represent the entire universe without needing a memory many times the size of the entire universe, how to calculate the events of a meaningful amount if time before the heat-death of the universe, how to power your machine, etc. etc. Whether it's possible to gather the required information to load such a device is irrelevant.

The question Laplace asks is 'Should such a device exist, with a perfect knowledge of the entire universe, what's to stop it precisely predicting the future actions of myself (and others) which I assume to be the result of free will?' The reason Heisenberg is irrelevent to the discussion is because we don't need to build the machine - There is already a machine that has a perfect knowlege of the entire universe, and calculates its behaviour with perfect accuracy - the universe itself. Laplace's Demon is simply a metaphor for the (hypothesised) deterministic behaviour of the universe.

Heisenberg is only relevent to our attempts to copy the universe - it says nothing about whether or not the universe behaves deterministicly or not. A refutation of the consequences of Laplace's Demon should find some behaviour of the universe that is be impossible, not just intractable, to predict, even given perfect information.