I would personally start by creating (x)html/css files and then porting those into Joomla. That way, if you decide to change your cms you wont have to untangle all the Joomla code from the html.
I've only dabbled in Joomla so I can't really help on that front, but if your after a good (x)html/css tutorial pop over to
http://www.nettuts.com where they have a ton of fantastic resources.
[EDIT] These are a few of potential interest: