Id use photoshop and if you have flash mx use that for cool animations. Im no expert but those will get you started. Photoshop takes time to learn. But once you learn things become second handed.
i made my bottom brand new sig using paint. sure i didn't make any of the pictures myself, and i just cut pictures and pasted them where i wanted it, but i think it turned out pretty good. if you wanna make pro sigs, you gotta use photoshop.