In spite of what you may read on some spec pages, iOS 6 and higher devices can only sync with Intel Macs with Mac OS X 10.6.8 and higher.
This is also the minimum iOS supported by iTunes under the iPad 4th generation, Mini, iPod Touch 5th generation, and the iPhone 5.
iPad 2nd and 3rd generation, iPod Touch 4th generation, iPhone 4S, with iOS 5.x and earlier can sync with PowerPC Macs of at least 867 Mhz (1 Ghz is greater) with Mac OS X 10.5.8, which can be upgraded to from any version of Mac OS X 10.5 for free. It is strongly recommended you get a USB 2 card that is able to provide power to the iDevice, if you have a pre-USB 2.0 Mac. This is a possibility for some 15", 17" Powerbooks, and PowerMacs desktops.
The iTunes you can use with Mac OS X 10.5.8 is iTunes 10.6.3 which is available from: http://support.apple.com/kb/DL1575
Note: For Intel Mac users, iTunes 11, which is required for iOS 6 syncing is optional on Macs that don't need access to iOS 6 devices, through Mac OS X 10.8.5. In other words, if you have an iPad version 1, which can't update past iOS 5.1.1, and have Mac OS X 10.8.5 or earlier, you can stick with iTunes 10.6.3 and maintain cover flow and other features if you so desire.
The original iPad, the 3rd generation and older iPod Touch, and iPhone 3GS and earlier all also support Mac OS X 10.4.11 and earlier on PowerPC Macs, when they have iOS 3.2 and earlier installed and the version of iTunes available at that time.
Once upgraded, iDevices can't have the clock turned back in terms of iOS at this present time, and that will limit them to the Mac OS X and Mac they can sync with as stated above.
If you feel there is a need for this, please post feedback.
You may also go to http://www.apple.com/recycling/ to get a fair value for your device if you find you can't use it anymore and it is past its
return/exchange period from the store you bought it at.