Unless they've changed the format of the data files in the mac-version for some unfathomable reason it should be enough to have the mac-version of the game, since KotorTool doesn't need the game executable in order to load the data files. You may have to set some paths manually to where the game is, since you'll be missing the relevant Registry keys.
If you have an intel-based Mac you should also be able to install and run Windows directly on it without needing Virtual PC. Windows XP should be enough if you download and install the Microsoft .NET Framework v2.0 on it.
Either way it's going to take some effort to get it running. I don't think you can run KotorTool on a mac without running it through Windows. If I remember correctly there is a 3rd party .NET Framework implementation for Mac OS X, but last I heard it wasn't complete, and it would only work if the application was written entirely in managed (platform-independent) code, which I'm not sure KotorTool is.