I tried opening a newer DWG file in Illustrator and the program flat out told me I could not do this. Though with older DWG (AUTO CAD) files I had no problem opening them in Illustrator. It's actually great because it not olny opens the file, when placed, but it converts all the lines into working paths.
You can't. In order to open newer DWG files, Adobe would have to license the relevant code from Autodesk, since they no longer make it available for free, which apparently they are not willing to do....
DWG is a proprietary format of Autodesk. Adobe's use of the DWG format comes from the Open Design Alliance.
Having said that, a decent workaround is DraftSight.
I use it for converting down to a lower DWG format. I haven't tried the Mac Beta, but am going to download it soon for my Mac. I currently use it on my PC, and transfer DWG file to Mac CS6.