This 'from the couch' video gives ideas on how to go about doing a 'mood board' in the early design phases: http://www.from-the-couch.com/post.cfm/title/creating-an-effective-mood-board
Basically:
* create a wireframe layout
* pick colour themes
* find inspirational ideas / design / websites (and write in detail why they are)
* find textures / images that will set the 'mood'
* put together all of it in a clean professional doco to present to the client
