Realistic Rain?

Hi, I was looking around, and I can’t seem to find a realistic rain effect using simple lines in flash mx?

All I was looking for is a diagonal down left rain effect using white lines which vary in size and alpha, anyone got any ideas?

Also, not sure if this is hard or not, but I need the rain to appear inside a mask, so that it doesn’t “rain” all over the page, just in one area?

All help is much appreciated.