I'm trying to take a number of circle-shaped objects of different radii and evenly spread them out over one plane, so none of them overlap.  I want them to be roughly centered around one point.

For example, see:  http://alignedleft.com/projects/2008/spacing-objects-question.png

The physics libraries are helpful at "pulling" them toward a central point (attraction force), and others have figured out how to calculate collisions (to bounce objects off each other), but all I want is to evenly distribute the objects in space — no "collisions" or "gravity," except that I need them to be grouped around one central point.

An added bonus would be to have the larger circles at the center, and smaller ones floating toward the outside, but that's not necessary.

Any thoughts on how to approach this?  Thanks!

You can use the physics library to get what you want, you just need to have both attractive and repulsive forces.

e.g. http://www.hardcorepawn.com/ParticleBox/

I got it working without physics!  I have a detailed write up on the final solution here:

http://alignedleft.com/blog/2008/11/how-to-cluster-circles-of-different-sizes-while-preventing-overlap/