Simulate Electric field

Hi All,
I am trying to simulate electric field lines between two different charges, charges can be similar or dissimilar.

I have a sample representing what I need

http://phet.colorado.edu/sims/charges-and-fields/charges-and-fields.swf

I only need to rotate the arrows as and when the charges are changed or distance between the charges are changed.

Any help in this direction would be appreciated.