I have written a tutorial on how to produce colored comic strip from script to finished image, using pencils, ink, paper, scanner, and the Gimp. It, of course, suffers from the fact that I am myself fairly new to this stuff, but – there it is. I hope someone finds it useful.
Drawing a speech bubble
Did you try inkscape for this kind of work?
As much as I love my gimp, but for this inkscape is far easier to use.
http://www.inkscape.org/screenshots/gallery/inkscape-0.45-comics.png
If you search the net, you will find some good -more detailed- howtos.
I had presumed that a vector graphics program would be unsuitable (except perhaps for the lettering and ballooning part). A coworker, in fact, recommended it at first but then withdrew the recommendation after he learned I inked on paper.
I have also been recommended Krita. It certainly has the advantage over Gimp that it supports CMYK properly. Still, Gimp is what I’m using now, mainly because that had the least learning curve for me, considering that I already was somewhat familiar with it.