Type 'Boot Camp Assistant' in spotlight and follow the instructions. You will need a Windows instillation disk or a Windows disk image file to install boot camp. Then the next time you start up your mac hold the option key. After you see two drives popup choose Windows. Now you have to use your Mac OS X instillation disk to install the boot camp drivers on windows. After that you should be set to install steam and MNC.
You can get XP for under $100 now. There are also places you can find installation disks/keys for free but I don't think Uber would appreciate us posting links on their forums.