another option is to use a theme framework. it becomes your main theme, and you create a CHILD THEME, with your desired style. I'd say that, if you are going to learn how to create a theme from scratch, learn how to work with a theme framework instead. They are a high quality base you can use as a starting point, are easier to work with, and are here to stay. Not to mention that once you get the hang of building child themes, building a second completely different theme will be much faster than starting another theme from scratch.
i prefer HYBRID, but there are comparisons of the main theme frameworks here:
http://www.wptavern.com/comparisons-between-most-popular-theme-frameworks,
http://www.smashingmagazine.com/2009/05/27/wordpress-theme-development-frameworks/
if you are going to build it from scratch, here is a PSD starting point:
http://www.area381.com/2007/07/10/wordpress-psd-framework/
and here is a very complete guide on building WP themes:
http://tr.im/sFsT