Catalyst works with Firewoks, via Firework's "Export FXG" feature. Unfortunately the FXG support in Fireworks CS4 has a lot of issues. It will be fully supported with Fireworks CS 5.
This is really only half of an answer. As a long-time Fireworks user I'm very confused by the approach and communication about the relationship between these two products. As an Interaction Designer, Fireworks has been my tool of choice for years. Over time, it has evolved into more and more of a prototyping tool. It has all kinds of nifty things like pages, states, and layers that are critical to how I work. Now you have this new product that I've seen in videos is apparently a tool specifically for Interaction Designers. It even has a default panel with a tab with the word "WIREFRAME" in it. It has things like pages, states and layers just like Fireworks. But, there's no clear story and clearly not a lot of support for how these two, obviously related tools, work together.
You're implying that it's on the Fireworks team to add support in CS5, and on the Fireworks side I see that there are some things that are on the Catalyst team to add support for. I know that Fireworks will be able to export FXG that describes pages/states/layers. So, the question is, will Catalyst correctly read and render it? Will I be able to roundtrip like you support with Illustrator and Photoshop? If not soon, when? CS5? CS6? I don't really care about your inter-product squabbles, I just want a clear picture of what the plan is.
I like the idea of Catalyst, but I don't want to waste my time on a product that is a dead end for me on the vague hope of future integration. Ideally, they will turn out to be great complementary tools, but right now it seems like the Catalyst team is surprised that there's even this other product called Fireworks, or have any insight into what it does. If Fireworks is the dead end for me I would be very sad, but so be it. What I care more about is wasting my time on tools that are going nowhere, or duplicating my effort because Adobe doesn't know what it's doing.
Please get your act together and get your story straight.
Couldn't agree more with Adam's comments, but there seems to be a little bit of light on the horizon - see the new FXG export script released here: http://labs.adobe.com/technologies/flashcatalyst/fireworksexport.html
More generally, I find it bizarre that the best supported graphics tool for round trip editing with Flash Catalyst is Illustrator. Illustrator would have to be a very distant third choice after Fireworks and Photoshop for this purpose.
C'mon Adobe, you've got the basis of an absolutely killer product in Fireworks, the toolset and features are excellent, but you need to address the multitude of bugs, sluggish performance and you absolutely must make it work seamlessly with Fireworks. Just ask your friends at Cooper Interactive, who are spruiking Fireworks for you, what should be the preferred graphics editor for round-tripping with Flash Catalyst!