To get DOF with layer mask  first duplicate the background layer.

Add layer mask to copy layer. 

In channel palette click on alpha channel and CTRL+I to invert it.

CTRL+A to select all and CTRC+C to copy.

In layers palette ALT+click on mask icon of copy layer. Document will turn into black, that is your current mask. CTRL+V to paste the alpha channel.

ALT+click again on mask icon to get back to your image.

Thats it basicaly, I dont know what you have. But if its not enough blured, use Gaussian blur slightly :)

I hope it will help :)

Miss Nancy Im sure that nobody on this forum who is regular was rude to anyone :)

Tihomir

Open your mind and share the knowledge!