IReader review has a good article on the ins and outs of iBooks new self-publishing option. The “kicker” is that in order to do it you have to have a Mac.
The Mac requirement is an exceedingly annoying one. It’s the same with making games for the iPhone – you must have a Mac. The solution is to work with an iBookstore Aggregator.
The article then goes on to discuss aggregators and tells you where to find them.
Enjoy your new Mac!