It's the same for me, too.  I've never been able to quit by just trying to force myself to stop daydreaming.  I posted some common things that people have suggested along the right side of the main page.  The only time I daydream less is when I'm too busy doing things in the outside world.  Try to find something that you like enough that will distract you out of daydreaming.  Definitely don't put yourself down when you do daydream.  That will only make it worse.