Attached Link: http://www.weirdass.net

Don't know how this will turn out for ya, but off the top of me head- Create a series of radial gradients on a new layer in photoshop. general size and shape of your dust cloud. Copy it to the clipboard, paste into a new doc. Convert to bitmap, pretty coarse setting. Convert it back to rgb, motion blur of about 10. Invert it, and paste it over your image (new layer) set to color dodge about 5-15%. Repeat layering and blurring. Also try a layer set to screen with the dodge layer over it for a cloudy effect. Good luck Mitch