Moving background. Better ideas? How?

The “classic” method to make moving background (clouds or smoke) is in Kirupa’s tutorial. The movement from one side to another can be done in AS. But I have experienced difficulties especially the background image is large, maybe 500px or more wide. The movement of such a large bitmap makes the movie not so smooth.
Has anybody any ideas to create such movements (especially clouds and smoke) in other methods?
Any example? tutorial? something?

Thanks
mx-guest2004