Hi. I have been a life-long traditional illustrator working with watercolors and/or pen and ink. I am now in the process of evolving. I want to create my illustrations within the computer via a Wacom Intuos 4 large tablet and Adobe Photoshop/Illustrator CS4.
I am writing this esteemed forum with the request to be directed to online training that would specifically help me with this transition.
With raster paintings it's easier just to pick up the brush, set a color, maybe a brush type (eg, airbrush, pencil, watercolor, etc) and just paint away. Before you start painting you MUST define the size of your illustration and need to think about whether you want to print it or not, and if so, then what size. You cannot scale UP your painting afterward without degrading the image quality.
Vector illustrations are much more elaborate (and harder to learn to be proficient) and you cannot just leisurely just paint away, as in PS for example. However, you can scale up or down your illustration to just about any size you want without any degradation to the quality of your work.
You can see excellent technical illustrations here with a combination of AI and PS: http://www.khulsey.com/
For some artwork (like the cutaway cars), he creates the outlines in Illustrator and colors them in PS.
I would highly recommend Painter. It emulates watercolors (and other paint) as well as papers and brushes. I know you hate to buy another app, but I believe it to be the right tool if you want to 'feel' like you are painting.
Check out some of the Painter sites to see what is possible.