Very similar to what Michael mentioned (2d Working Model) only this one is free it's called Algodoo http://www.algodoo.com and I think you can import accurate shapes, not sure, you'll have to check it out.
it's a pretty straight forward, drag&drop application. the output is a script(thyme), which you can paste into algodoo (shortcut F10 in algodoo brings down the console window). i did use it with some older versions of algodoo, but as i can recall, dxf2phun is quite picky regarding the geometry it's been fed. i had more luck with svg2phun