well, i'm working alot of hours right now, and taking a particle class online in my spare time, so I'm not too sure if I'll have time to take a stab at setting this up for you. Besides, if me or someone else does it, YOU won't learn how to do it.

We'll help you out, though, but you should definitely be the one doing the tweaking.
the biggest problem I'm seeing so far with your shot is that the particles stick to the top while it shakes, and then all of a sudden come bursting off in every direction with tons of force. They look like swarms of bugs or pressurized water sprays or something. Something that has it's own power propelling it. Dust doesn't have any power pushing it, but rides air currents as gravity pulls it downwards.
something to try would be emitting on the first frame from the top faces of the geometry, then letting forces handle all the animation from that point on. Definitely have a gravity in there, and at least 1 or 2 wind space warps with strength set to 0, each with different settings in turbulence, frequency, and scale. and keep the scales small, like 0.1 or 0.05. You may need a drag, too so they don't fall to fast, or maybe just turn down the influence of the gravity (it defaults in PFlow at 1000%). Oh, and don't forget to have your box geometry set as a Udeflector.
That's what I would do right off the bat, and I'd start tweaking from there. There may be some issues with emitting from the same geometry you're using as a deflector, in which case you may want to make some non-renderable geometry to emit from that is slightly above the actual top face of the box geometry.
Anyway, there's some ideas to try. the main thing is to NOT give the particles a speed operator, let space warps (mostly gravity) do all the animating.