Heather has a great new article on customizing the SharePoint user interface. Like her, I wish I could give you a step-by-step guide on how to do it but there's just no simple solution (here are a few tips to get you started ). In Heather's words:
Customizing SharePoint is like riding a bike, it is very hard to tell someone how to do it, and that person really just has to try, fall down, try again, and they will figure it out.
I couldn't agree more.