RedSn0w Updated to Fix Issue on OS X 10.5.x
The iPhone Dev-Team has released an update to RedSn0w that fixes an issue for those on Mac OS X 10.5.x or earlier.
Update #1b: The OS X version of redsn0w has been updated to fix an issue for those running OS X 10.5.x or earlier.
You can download the new version of RedSn0w from here. You can find instructions on how to jailbreak your iOS device here.