How can I run Warcraft III (a PowerPC app) on OS X Mountain Lion?
Solution 1:
Two ideas I can think of. First, dual boot with OS X 10.6, which still supports Rosetta.
The other is to obtain a copy of Snow Leopard Server, which had a license which allowed you to run it in a virtual machine. (The license for normal SL did not allow you to run it in a VM. Lion and Mountain Lion changed the license to allow it.) Then use Parallels or VMWare Fusion to run it. However, I don't believe the graphic support is very good with guest OS X machines, so it may not run well.
Even if you can find a way to install the app, IIRC Warcraft III was a PPC binary for the game as well, so you'd still be stuck.
Solution 2:
The short answer is: You can't run PowerPC apps on ML. But as already suggested there are alternatives. Parallels or VMWare for example and a Windows Virtual Machine may allow you to run a relatively old game with decent framerate. (if you have the Windows Version, tho Blizzard games used to be win/mac on the same CD).
There's no way to install Rosetta (to run PPC code) on a ML because there were lots of underlying changes that make this an impossible task. I don't know if people have found ways to do it, but it's certainly "hacky".
Solution 3:
If you can get a copy of Warcraft III installed on another Mac, you should be able to run it just fine under any version of OS X, including Mavericks (10.9). The trick is finding a machine still running a version of OS X old enough to support the Rosetta environment. For this, you will need a Snow Leopard or older version of the OS and an Intel machine. Once you have it installed and updated to the very latest, you should be able to copy the entire Warcraft III directory from that machine to your current machine. You may have to re-enter your CD code, but that should be the easy part.
And yes, this has been tested. I restored my copy of Warcraft III and the Frozen Throne expansion from an old backup to a 2014 retina MacBook Pro running Mavericks 10.9.4 and I was able to launch and get into a local game.
Update: only local games will work under Mavericks and later. This is because WC III uses OpenTransport for it's networking, but Apple has removed OpenTransport support starting with Mavericks. If you only want to play against the AI, this won't be an issue. But for everyone else, this is less than ideal.