I recommend learning it ASAP - eventually support for standard HTML will become depreciated, and XHTML will be the only code supported. Which means you have to learn CSS.
I recommend
http:/www.yourhtmlsource.com/ - it's brilliant. I managed to create a fully functioning web page, with JavaScript menus and everything, using only that site. And it's proper XHTML, as approved by
http://validator.w3.org/.