Are you sure it's dust and not bubbling of the underlying finish? Usually I wait a while between sanding and painting, and the dust clears by the time I'm ready to paint. Normal house dust falling into the paint is no big deal, if you don't panic about it. The paint "skins over" so fast that the dust doesn't really stick ... it can be rubbed off later on when the paint is really dry. It you think you're leaving too much dust on the surface after sanding, get a "Tack Rag" to wipe the surface clean before painting.

Phil