You'll find Photoshop the best for manipulating images anyway
Fireworks is more of a web based program used to build simple webpages using simple graphics which can then be lowered down in qulaity and such for webpages, so doesn't have the wide varierity of choices Photoshop has (though still has some effects),
I also don't think its as user friendly for making images as Photoshop though which is weird you think the other way
though its definetly easier to draw in Fireworks than Photoshop since it uses the same type of interface as Flash does, as you can draw properly (Macromedia), rather than Photoshop that uses aqward shapes and weird layers which makes it very hard to make complex images without a program alongside with it if you wanted to do some designing as well as image manipulating.
Though i'd say Photoshop to manuipulate effects (better all round really),
and using Fireworks to make the vector images you might need to make complex images if you need them (I use Flash to do this, though still uses Vector since its built by Macromedia).
Then you'd save out of Photoshop with the manipulated image, and go back into Fireworks, where you'd build the website using the images you have made in both together, and lower quality if need be for dialup connections, and that'd be rather kewl, so each one has its own special qualities.
i hope this helps
BanChan I agree
Those sigs are excellent!!!