Nick Daws had U.K. freelancer David Robinson as a guest blogger recently. David Robinson has written two books on formatting an ebook: E-book Formatting and Publishing on the Kindle and E-book Formatting and Publishing on Smashwords.
Robinson's blog post covers using MS Word to prepare your ebook to upload to the Kindle Store and to Smashwords. It's important to have your ebook in perfect shape before you upload it to make sure you'll pass the vetting process. Not passing vetting can add extra time to how long it will take to get your ebook into your readers' hands.
If you need help getting that ebook into shape read David Robinson's post at Nick's Writing Blog: The Secret of Successful E-book Formatting.