It's official. Of note, anyone that buys a Mac on or after October 1st is eligible to upgrade to Leopard for only $10.00. The Mac must be purchased from Apple or an Apple Authorized Reseller. That means you have to buy a brand new computer. It may be best to call Apple for details.
Why buy now? As I said before, you'll be able to run TWO operating systems as opposed to one if you buy now. There is an advantage to this.
Here's a link to Apple's website that lists Leopard's system requirements.
Erik