Update on my previous post. GNS3 will now work under Mac OS X – but there are some steps to do:

1. Download the version with Python included
2. Once installed, use the old dynamips from 0.5 (or at least the last working one for you)
   Click on your old (working) GNS3 -> show package contents -> Contents/Resources and copy the dynamips-0.2.8-RC2-OSX-Leopard.intel.bin to the corresponding folder in your new GNS3 package.

Now start GNS3 and see if everything is working. It is, at least for me.