A good place to start learning HTML and CSS (a definite must to make xanga skins, or atleast good ones!) would be:

http://www.pageresource.com/

Very straightforward and with the "Newbie" in mind. And once you're comfotable with these two languages, heres the w3 specifications (w3 is the governing body that overlooks web standards):

html4: http://www.w3.org/TR/html4/
css2: http://www.w3.org/TR/CSS21/

ok thanks.

or go here.

http://www.yourhtmlsource.com/

....
[ http://www.htmlgoodies.com ] <- Beginner
[ http://www.developer.com ] <- Really advanced... -shrug-

I think it would be best to put these in the BBoR. I'll do it now. :D