Digital Tweaker:

Anyone can create a book for iBooks with Apple releasing the iBooks Author app in the Mac Store. It uses simple drag and drop features with Word files and images so that everything is done for you. Since iBooks Author requires you to have OS X Lion installed, it makes it difficult for those of us who have not upgraded from Snow Leopard yet.Here is how you can get around that and install iBooks Author on Snow Leopard.

I haven’t tried this yet but I’ve heard it works.