Welcome to Linux Questions!
Yes, Shrink your Mac partitions and leave as much free space as you want for Fedora.
And check if your system is supported-
ioreg -l -p IODeviceTree | grep firmware-abi
If this returns “Firmware-abi” = < “EFI64″> then your system is supported.
When you have some time it would help your to read the Fedora 18 documentation before you install Fedora.
It helped me to read the Fedora 17 documentation while I was in the middle of the install- -
Webpages to help:
Fedora 18 On A Mac Book Pro:
And this is a good page but for Fedora 17
Hope this helps