Currently Being ModeratedNov 29, 2012 5:29 AM (in response to hoosier55)
You don't. Apple only makes their iBook Reader app for their iOS devices, not for their computers. eBooks purchased through the iBook store are DRM locked to Apple's iBook reader so cannot be transferred to another reader program.
If you want to read ebooks on a Mac, then do not buy them from the iBook store. Get one of the other readers - Kobo reader (by Kobo books), Nook reader (by Barnes & Nobel) or the Kindle reader (by Amazon) - all of these companies sell ereaders, but also make their ereader apps for OS X, Windows, iOS and Android.
Currently Being ModeratedNov 29, 2012 5:51 AM (in response to hoosier55)
As Michael said, it is not possible for books with DRM, which what most people want to read. There are some books in the iBookstore which do not have DRM, e.g. most free books and those from O'Reilly or Take Control. These can be read on your Mac using one of the standard epub reader apps for OS X.