You have a MacBook Pro, so it has an Intel processor. If Warcraft 3 is a PowerPC application, then it will not work on Macs that run Lion (10.7.x). Until Snow Leopard (10.6.x), Mac OS X had a "translator" called Rosetta that translated PowerPC code into Intel code, on the fly. So PowerPC apps would run on Intel Macs, with a small performance penalty due to Rosetta doing its thing. Lion no longer supports Rosetta.
This web page has some info about Warcraft 3 supporting Lion.
http://www.lancraftwc3.com/2011/08/warcraft-3-mac-os-x-107-support.html
If you have an external drive, you could install Snow Leopard (10.6.8) on it, select it as the startup disk and start up from it, and install Warcraft 3 on it. But this would only work if your MacBook Pro is an older model (not a brand new one that came with Lion pre-installed).