Josh, the other designer at clevermethod, really pushed for us to be using Adobe Fireworks when designing for web. I was reluctant at first, unfamiliar with the program and frustrated when trying to use it. But since I hate using photoshop for web, and using illustrator doesn’t make too much sense (I used to use Illustrator because of my hatred for photoshop for web design), I am now a fan of using fw for web. In fact, I believe those who use photoshop are amateurs. Photoshop is for editing PHOTOS. ha.
In fireworks you can have pages, and states of those pages. You can create animations too. Here is an article about refining your designs in Fireworks by Smashing Magazine.
I highly suggest you try it out.