It should run fine under OS X after you've launched Classic. It won't run natively under X, but I'm pretty sure the basic Classic setup has all the necessary extensions to play it. It runs fine on my Mac (although I'm running Panther 10.3 instead of Leopard)
Classic is built in. Go to your System Preferences and you'll see Classic in one of the rows. It's either the Classic Mac or the System 9 logo. You just need to set it up and launch it. It runs in the background and only comes into use when you launch a classic application.
You should get a dialog box when you try to launch SWC asking you about classic as well.