My personal preference for learning html and CSS is using online tutorials or a book, but using Notepad to code it. That way, you learn the coding structure without Dream Weaver telling you what the answer is as soon as you start to type it. Though it isn't color-coded, it will help you remember how to do it.
As for GIMP, there are thousands of online tutorials out there for it. That is really the only way to learn computer graphics. If you get good enough with GIMP, then it can be just as powerful for beginner - intermediate graphics. However, for easier navigation and more power, I would suggest investing in Photoshop (CS or CS2) in the near future.