I would definetly recommend this site to learn about all kinds of web technology:
http://webstandards.org/learn/ .
I would start by learning xhtml 1.1 strict, it is the most advanced standard on the block right now. But the great thing, is that compared to html 4.01, xhtml is quite simplified - there are less tags to learn and less attributes to remember. Basic xhtml shouldn't take much more then a day or two to learn, there isn't a very steep learning curve.
Once you get down xhtml, the next step to take is CSS, or cascading style sheets. You use CSS to style your xhtml, the xhtml itself should be very bland and to the point, CSS is where you should really get into giving a site visual beauty.
xhtml is much simpler then css, but to learn both I would recommend you just trudge through and do your best to code your site with the two languages. If you run into trouble, make a small case study, to experiment with different properties of the languages until you can work through and fix the problem. And there are tons of resources on the web - discussion boards, weblogs, and mailing lists. There is all the information you need on the web, and even more you can buy at bookstores.