Depth of field is purely a function of focal length, aperture and DISTANCE from the subject. It's the same for digital or film.
What you are probably seeing (or being confused by) is the "crop factor" that most pro-sumer digital cameras have. Let me try to explain...
If you fill the frame with your subject, say at 10 feet, with your lens and a film camera you have a certain depth of field at the aperture used. If you used your digital camera AT THE SAME DISTANCE, 10 feet, the dof would be the same.
So what would be different? Well thanks to the crop factor on most digital cameras, your subject would be a lot larger in the viewfinder with digital than with film. Meaning that if you position yourself (distance-wise) so that the image fills the same area of your viewfinder with digital as with film, you would be FURTHER AWAY from your subject. And since you are further away, you get a greater dof.
Does this help?