If you download the ePub version and can read it on a PC/Mac using Adobe Digital Editions, then you can also read it on the iPad using
Bluefire Reader.
To read the ePub with the Kindle app, you need to a) strip the Adobe DRM, and b) convert from ePub to MOBI. If you add a 3rd party plugin from the tools_v3.1 bundle to Calibre, it will do both (a) and (b) for you. As usual, see Apprentice Alf's Blog for DRM info (start with the oldest post).