Theme Design

I don’t know how helpful this will be as it was written with GIMP in mind, but I wrote a series of tutorials (Squidoo lenses) that take the reader from the digital mock up of the site to conversion to a stand alone WordPress theme. The first part is Creating a Fancy Website Layout in Gimp 2.6, but if your theme is already designed, you can check out the second part, How To Slice Up Graphics for XHTML and CSS or even Converting a Static HTML Site into a WordPress Theme- Part 1.

The final tutorial mentioned has links to similar tutorials written by other authors as well.

Good luck and I hope this helps.