Spray paint effect in flash

hi.
I was just wondering if anyone knew how to creat the kinda smoke effect you get when spray painting. The kindof effect that it is kind shot out of the bottle, then when it hits something it spreads all over the surface? Also if as is involved (begginer complex stuff, not simple things…) then pls explain how it works.

Thanks.

P.S. I tried just a load of xpanding circles (with differenct sizes ect.) but didnt really look good…

edit: hehe i searched it in google and theres loadz of ppl who asked the same question, most of em have the answers but all the ones i found were in other programs (like swish).