Fireworks is ace for buttons and the like, Fireworks is my tool of choice, although i'm still in the dark ages with version 3.
Gimp will do you buttons, but without the finesse of something like Fireworks which is built for that purpose.
Best way to do buttons is use CSS, and lay an inline list over the graphic/s. Gets the same effect, nearly, with little bandwidth.
Create a 1x1 gif of your desired colour then stretch it under all the CSS links, job done. It can be quite hard, but easy way is to get a decent CSS template and modify it.
http://www.freecsstemplates.org/css-templates/