Well, smoothly if you are running EXS with no filters, most of the internal instruments other than Sculpture, which with the right patch can bring most current Mac Pros (and in says, and current laptops) to their knees (overloaded with core audio errors, so no playback).
Really, I'd either save for a better one, or have you considered a Mac Mini? You can upgrade it to a full i7 sandy bridge CPU quad core, and put a bunch of ram in it, your much better off than the laptop.