There are several advantages to designing using CSS instead of the usual tables. Among these advantages are the following:
- Write faster loading, dramatically smaller pages
- Speed up site maintenance by separating the content from the layout
- Write Device-independent pages that will work on everything from a PC to an Internet-enabled refrigerator
- Write search-engine friendly pages that can actually be understood by search-engine spiders
- Write more accessible code, which is now a legal requirement in some countries
This site provides information about how to design using CSS instead of tables, offers a free chapter for download, and offers this book for same. Worth checking out.