Ripped right off autocad product requirement page, relevant info bolded for convienance:
For AutoCAD 2013 for Mac
Apple® Mac OS® X v10.8.0 or later (Mountain Lion), OS X v10.7.2 or later (Lion), or OS X v10.6.8 or later (Snow Leopard) with 64-bit Intel processor
Apple® Mac® Pro 4.1 or later; MacBook® Pro 5.1 or later (MacBook Pro 6.1 or later recommended); iMac® 8.1 or later (iMac 11.1 or later recommended); Mac® mini 3.1 or later (Mac mini 4.1 or later recommended); MacBook Air® 2.1 or later; MacBook® 5.1 or later (MacBook 7.1 or later recommended)
3 GB of RAM (4 GB recommended)
2.5 GB free disk space for download and installation (3 GB recommended)
All graphics cards on supported hardware
1,280 x 800 display with true color...