enabling snow extra effect in compiz

install Compiz Config Settings Manager

System -> Administration -> Synaptic Package Manager

and search ccsm (Compiz Config Settings Manager)

install simple-ccsm

and compiz-fusion-plugins-unsupported

Then goto System Preferences -> Compiz Config Settings Manager

Extras-> enable Snow

then press Win key and F3 (Special Key and F3)
you will see the snow