I've been playing with Joomla for over a year now... I'll show off my latest site on Friday if anyone's interested 🙂
I was asking the same questions as you all were.
favicon.ico - create a gif in photoshop you want to replace. Upload it, then rename it using an FTP program to filename.ico
To edit look & feel, always template_css.css file.
Get the firefox web dev toolbar, you can find all the div IDs.
Get a book on PHP for beginners as well, you'll gain a better understanding. Also if your knowledge isn't great on CSS - get a book on that as well.
Joomla has a great community, and they will help you no end with what ever help you need. Any problems that do occur, 99% of the time has happened to someone else, so just do a forum search with the error.
I'll be glad to help if you need it, drop me a PM on this.