Is it possible to dual boot Mac OS X Snow Leopard and Fedora 17?
If you've successfully installed Fedora on a free partition, the rest is easy. Just download an ISO  copy of rEFIt and burn it with Disk Utility to a blank DVD.  Then, while booting, hold down C after the chime to boot to rEFIt.  It will give you the option to boot to Linux (this is indicated by a Tux icon).  

Additionally, rEFIt is able to install itself to your system without a DVD boot every time, but I couldn't recommend it as I had some issues with this personally.