You could strat with low density Grid mesh (10x10). Subdivide Multi Fractal (W menu) with subdivisions of 2 and factor of 20-30. After that you could scale the grid back to flat.
Select the edge loop that will split the paper in half and press V to rip.
Repeat for any new parts that you decide to have.
Optionally you can create cuts in diferent direction by using Knife tool (SHIFT+K).
To animate - select all and press P to separate All Lose Parts. This will give you an object for every piece.
It is good to texture your paper before starting the cutting operations.
Thank you, I will try that. Do you know how i can get a realistic effect of the way the rips look? I know the paper will probably have to overlap, and i wonder if there is some way to make the white edges more transparent if possible.

Someone did something like this with a glass cup here on blenderartists awhile ago. If I remember they modelled all the pieces seperately, stuck them together to form the cup, shoved it all in the BGE, recorded the IPO(s) of it breaking apart, and then played that in reverse.
Seems to me that would be your best bet. Do a bit of research as the BGE and animating are not something I’ve messed around with much…despite being the sole reasons I picked up 3d in the first place lol. What can i say…modeling is fun and texturing is MORE fun.
With the steps provided above here are two variants of paper ripping animation (just quick demonstration): http://www.youtube.com/watch?v=g70B2YRtSww
The blend files attached below.
The model of paper is really low detail but with some handmade alpha textures you can create nice jagged edges for your render.
This tutorial might help: http://www.pixeldigest.com/ripped_paper.html