On the Joomla community site there's a recent post made of a video from the Joomla Day conference in Australia about creating a Joomla template from scratch. The presenter is Norm Douglas.
Norm Douglas recently presented about how to create a Joomla template from scratch at the Joomla Day in Melbourne, Australia, on 13 February 2010. This is a very informative 77 minute presentation and also covers using the Firebug Firefox addon, code editors and much more.
He covers some simple tools you get you started, the basics of HTML to create a sample layout and looks at CSS definitions that can make the layout look a bit better. Firebug (the plugin for Firefox) helps make locating the different parts of the page easier with a highlighting feature.