Currently, you have to use another program to convert your text files to EPUB format for uploading to the iTunes servers using QuickTime. While I have not yet done yet this myself, I think I can help you through the steps as I understand them. After your file is ready to submit you also need to run it by a EpubCheck 1.0.5 or greater file inspection program. At that point you are ready to upload your iBook to Apple using QuickTime.
via Macsimum News – Greg’s bite: How to publish an Apple iBook.