From HTML to XHTML is just a matter of closing tags specifying, having lower case tags, and specifying a few extra things in the top of your document. Pretty simple.

When you take that into making tableless layouts what you I recommend is go simple. Learn how to make 2 and 3 column layouts and then from there move on.

From PSD to a tableless CSS layout its pretty much the same you slice the images you need and hand code it just without using tables. Of course you need to know how to code without using tables first.

EDIT: EVERY TAG NEEDS CLOSING (reply to the post right above).