I highly, highly recommend using the Zen starter theme. It's blank (as far as most of the design is concerned) but it has a lot of documentation, and a lot of the CSS styles pre-defined for you so you don't have to hunt them down.
Drupal can be a little frustrating when you have to hunt down that one CSS selector that is included in core that you can't seem to override for some reason. Zen has them all pre-listed.
It also has all of the hooks you need in order to "graduate" to higher-level theming, with superb, full documentation.
It has saved me countless hours of work...even when starting a theme from absolute scratch (e.g. a Photoshop template or a pre-designed XHTML/CSS site).
Good luck, and do come back and post any questions you might have!
Mike