Apple decided to limit the use of the application to Lion Author iBooks. Here’s a way to install Snow Leopard. This proves that the restriction is artificial.
Following the release of new software from Apple iBooks Author, some users have seen frustrated not being able to install it in Snow Leopard.
Yet it is well to do and the software is fully functional.
First , locate the document SystemVersion.plist located in / System / Library / CoreServices
Make a copy on the desktop and also make a backup copy.
Open the document copied to the desktop in a text editor and change the two lines 10.6.8 in 10.7.2. Replace the document in the system by the amended document on the desktop and restart
Download Author iBooks in the App Store.
Replace the document SystemVersion.plist copied to the system with the backup document remains on standby to keep the same name of course .
Now locate Author.app iBooks installed in the / Applications folder.
Right click to display the contents of the application and locate the document Info.plist. Open the document Info.plist in a text editor and look for the line LSMinimumSystemVersion 10.7.2 and 10.6.8 replace LSMinimumSystemVersion.
Save, that’s over Author iBooks run perfectly with Snow Leopard.
[UPDATE] Hack tested successfully, the important thing is to quit the AppStore first before changing the plist file. Remember to submit the original or you have any problems with future updates of software.