Offering Ebooks as Downloads

I have an ebook project I want to put on my WordPress site for download.

I would like to offer them as .epub files to be read on Stanza and other ebook readers.

How do I put this up as a downloadable link? I’ve tried doing the Media Library thing, but I’m getting a “File type does not meet security guidelines. Try another.” error.

I would also like to link the file to a cover image.

Can someone help me? I looked at one post that said something about a text widget, but I couldn’t get that to work either.