Folks, if the CD/DVD doesn't say "Mac OS X Install Disc" on the disc or doesn't have a huge "X" plastered across the disc (whatever the design for it's particular version of OS X), then it's not an official retail version of the installation discs. Any disc that you see sold that has either a colored background and doesn't have the "X" plastered on the disc is a disc that came SPECIFICALLY FOR THE SYSTEM IT SHIPPED WITH. People are selling these discs on eBay and other places and they are not meant to be sold without the Mac that it belongs to. THEY WILL MOST LIKELY NOT WORK ON ANY OTHER MAC OTHER THAN THE ONE THE DISCS ORIGINALLY CAM WITH!! If you see such discs, STAY AWAY! Only get the retail versions of the full installation or the upgrade if that's all you need. Not to difficult to grasp, folks.... 
Maybe this way people will pay attention and understand...
Common sense, people. If it looks too good to be true, it most likely is.