Autodesk today gives official support to running the Windows version of AutoCAD on the Macintosh computer, through BootCamp.
Sparse info here: usa.autodesk.com/products/mac-compatible-products
BootCamp is software that allows 32-bit programs locked to Windows XP and Vista to run on the Mac's OSX "Leopard" operating system. You don't need a special version of AutoCAD; what you need is a copy of XP or Vista that you install through BootCamp on your Mac. Then you install regular AutoCAD in the Windows environment permitted by BootCamp.