Yup, you need to be able to convert the book to either Word .doc or PDF (if you can print it, you can print from a Mac and choose Save As PDF...)
Not sure how many ebooks allow you to convert them or print them though... I only read the ones from Baen.com, and you can either convert them and mail them to yourself, or just use Safari to read the HTML versions online, but those are the only ones other than the out of copyright ones from Gutenburg that I know of that aren't DRM protected.