Apple has confirmed Leopard's revised system requirements -- which exclude 800MHz G4 Macs -- and were detailed earlier by AppleInsider. They are:
A Mac computer with an Intel, PowerPC G5, or PowerPC G4 (867MHz or faster) processor512MB of memoryDVD drive for installation9GB of available disk spaceSome features require a compatible Internet service provider; fees may apply.Some features require Apple's .Mac service; fees apply.
iChat 4.0 requirements
Audio chats require a microphone and a 56-Kbps Internet connection.Video chats require an iSight camera (built-in or external), USB video class (UVC) camera, or FireWire DV camcorder; and 128-Kbps upstream and downstream Internet connection.Photo Booth and backdrop effects require an Intel Core Duo or faster processor.Backdrop effects when using a DV camcorder require fixed focus, exposure, and white balance.Some iChat features offer better performance and quality with higher system capabilities.
Individual Leopard apps
Time Machine requires an additional hard drive (sold separately).Photo Booth requires an iSight camera (built-in or external), USB video class (UVC) camera, or FireWire DV camcorder; and an Intel or PowerPC G5 processor. Backdrop effects require an Intel Core Duo or faster processor. Backdrop effects when using a DV camcorder require fixed focus, exposure, and white balance.Boot Camp requires a Mac with an Intel processor and Windows XP Service Pack 2 or Windows Vista (sold separately).Screen sharing in iChat and in the Finder requires a 128-Kbps Internet connection (300-Kbps recommended).Front Row requires a Mac with built-in IR and an Apple Remote.DVD Player requires a 1.6GHz processor or faster for improved de-interlacing.Developer tools require 1GB of memory and an additional 3GB of available disk space.
Leopard upgrade options
Customers who purchase a qualifying new Macintosh computer on or after October 1, 2007 that does have not Mac OS X v10.5 Leopard included can upgrade to Leopard for $9.95 through Apple's Mac OS X Leopard Up-to-Date Program.
If you purchased multiple qualifying systems on a single invoice, you can either (1) purchase a Single-User Upgrade Kit for each qualifying product, at a cost of US$9.95*; or (2) purchase fewer Single-User Upgrade Kits and request the Right to Copy for the remaining qualifying products.
The maximum number of Up-To-Date packages that can be qualified from one individual appears to be 20.
Discounts on Leopard
Apple is offering Mac OS X Leopard for $129 with free delivery on October 26. However, there are several other online retailers who likely will not charge you sales tax and are also advertising hefty discounts.
For instance, Amazon.com is offering an instant $20 off Leopard, bringing the price down to $109.
MacMall is also offering $20 off the single license ($109) and $10 off the 5-seat family pack ($189). However, presently MacMall's website has the wrong pricing for Leopard and is offering the single license version for $20 off an incorrect retail price of $109, bringing the total down to $89. It's possible that MacMall may honor that price for readers who act quickly but it is not a certainty.
(Update: MacMall has corrected its error, the discounted price is back to $109).