insert the Leopard CD into your mac. Turn it on, after you hear the startup tone, hold down the C key, which will cause the mac to boot using the leopard CD. once it is booted, it will walk you through reinstalling Mac OS X.
try restarting your computer
Mac Leopard is not a person. It is a piece of desktop software developed for the Apple Mac computers. Its full name is Mac OS X Leopard and one can find more information on the Apple website.
Snow Leopard is an upgrade to Leopard and so you will need Leopard installed on your Mac before installing Snow Leopard. For Mac computers with an Intel processor running Tiger you will need to purchase the box set that includes iLife 09 and iWork. (See links below)
Likely never. Snow Leopard is a $29 upgrade to Leopard, but it requires a Mac with an Intel processor (newer than 2005) and 1 GB of RAM.
Mac "Lion" and Mac "Snow Leopard" refer to iterations of Apple's Mac OS X (operating system, version 10). "Lion" is the newest as of this writing, and is version 10.7, while "Snow Leopard" is its immediate predecessor, and is version 10.6.
Although technically an upgrade to Leopard (Mac OS X 10.5) the Snow Leopard (10.6) disc does have a full installer and so can install the software onto a blank formatted disc with no existing OS.
10.5, Snow Leopard is 10.6
To upgrade from Mac OS X 10.4 (Tiger) to 10.5 (Leopard) you will need to buy a boxed version of Mac OS X 10.5. If you have a Mac with an Intel processor you can go straight to Mac OS X 10.6 (Snow Leopard) which is a cheaper upgrade option.
Currently, it's $129 dollars (Mac OS X Leopard). Once Snow Leopard is available (August 28), it will be a $30 dollar upgrade from Mac OS X Leopard.
Although the appearance of Mac OS X 10.5 (Leopard) and Mac OS X 10.6 (Snow Leopard) is similar there are many differences in the workings of the two systems. Most notably Snow Leopard requires a Mac with an Intel processor whereas Leopard will run on earlier Macs with G4 or G5 Power PC processor as well as the newer Intel based Macs.
Mac OS X 10.6 (Snow Leopard) will not work on a Mac with a G4 processor as it requires an Intel processor based Mac. A G4 (867 MHz and faster) can run Mac OS X 10.5 (Leopard).
Mac OS X 10.5 is known as Leopard. The last available version of Leopard was 10.5.8.