This post acts as a reference to drupal theming.
Basically there is one choice as far as theming is concerned, you should choose whether you will start from scratch or you will install a 'ready' theme and customize it a bit to your preferences. This part will cover the second choice while the first choice will be covered in part 2. I must state again that this tutorial will act as a reference and only.
I am personally fond of choosing a theme where basically only the layout structure exists in its css.I am aware of two such themes.
The first theme is zen. Zen is an excellent starting point for themers that can offer extreme css customization due to the fact that it creates classes automaticaly for anything like taxonomy terms, front page, node id, node owner etc. Excellent documentation also exists and can be found here.
Another theme is the blueprint which is based on grids. The drupal redesign is based on the blueprint framework.More info for blueprint can be found here. A useful tool for creating your own blueprint theme is the contruct constructyourcss.com
i hope this will shed some light..