Have a look at these articles on CSS vs. Tables.
Article 1,
Article 2,
Article 3.
Use google and you will find hundreds more. Laying out pages with tables is easy, but not recommended any more. However, due to non-standard compliant browsers (i.e. IE) your pages may look differently in different browsers unless you get it absolutely right.
If you want to learn CSS, make use of
W3Schools. Also have a look at
CSSZenGarden to see the full power of CSS.

Select the style sheet from the right and see how the pages look totally different. The HTML page remains the same, but changing the css file can completely change looks. CSS Zen Garden is a truly remarkable site.
When you visit W3Schools, also pay attention to XHTML there. Its not too different from HTML, but certain rules are different.