The inexpensive gray Mac OS 10.5 Leopard DVDs which say "Mac Pro", "MacBook Pro", "MacBook" or "iMac" on them contain SYSTEM-SPECIFIC software installations and were meant for only the particular Macintosh they were sold with. They install some software components that your Mac cannot use or doesn't need. Many times, the OS software won't even install on your Mac. Hardcore Mac sells UNIVERSAL installation OS 10.5 Leopard DVDs which are always black with a range of purple hues toward the middle and have a large partially-shaded outlined black "X" on them. They are meant for ANY Macintosh that supports Mac OS X 10.5 and will install an appropriate version on your machine. Before you buy from another source, make sure you know exactly what you are getting. No matter what the seller says about them, system-specific versions have caused problems when used on other computer models. This is why they sell for less than the universal installers. Apple considers it a violation of their software license agreement when operating systems from gray CDs or DVDs are installed on machines other than the ones for which they were intended.