In case you didn't know, you can run Rhino3d on the Mac. It's funny because, like Autodesk who is now in the process of developing AutoCAD for the Mac, they once said there was no chance in hell they were ever going to write their app for the Mac platform. Well things have certainly changed because the Mac platform (OS X) has the fastest growing operating system user base out there.
I've been using the beta of Rhino for the Mac for about a year (but not enough to know it well at all), and it doesn't have all of the features that the PC side does (yet) but they are getting there. The good news is that you can use it for free until it's a fully released and supported product.
You can get it here. Once you fill out the form, you will get a download link.
Rhino3d running on the Mac