If you have access to a copy of Windows lying around, there's always the option of running the game in a virtual machine. Note that by running Windows in a virtual machine, you will naturally take a bit of a hit in performance. Give the virtual machine access to a large chunk of your system's resources and you should be fine though.
While I've never run games in a virtual machine myself (I use virtual machines principally for Linux installs), I checked out the community's forums and it looks like it is a fairly common task. It can be a daunting task for an inexperienced user, but the actual virtual machine application makes it a very simple process.
Another option would be to simply utilize Mac's Boot Camp to put a copy of Windows on another partition on your hard drive and run it from there. Both of these tasks though require a copy of Windows on hand, so if you're lacking in that area, my apologies.