Can ePub books be published to iBooks and then downloaded and displayed on a Windows PC and devices?

ePubs can be sold in the iBookstore : http://www.apple.com/itunes/working-itunes/sell-content/books/book-faq.html

the iBooks Store only accepts books created with iBooks Author (.ibooks) or books in the EPUB (.epub) format.

Whether they will be able to be read on a windows computer will depend upon the publisher - most publishers include digital rights management on their ibooks which tie them to the iBooks apps (iBooks is only available on iOS devices and Mac computers), if DRM isn't included (free ibooks tend not to have DRM, and some publishers don't include it) then you might be able to read them outside of the iBooks apps.