There have been numerous discussions of this here over the years. Here is one of the most informative and lively ones James
DIV and CSS is the way to go SEO-wise If you look at the cached view of websites programmed like this they look the cleanest and the search engines like it the best If you look at the cached view of pages that use an abundance of tables you will see how ugly it looks P.S. search engines LOVE Wordpress, and there are no tables in the code, only DIVs and CSS
Agree with many of the comments. Take a look at pages coded both ways. Then think about a search engine crawling it and what it is seeing. There is a place for both, but CSS can remove a great deal of coding from your page. Search engines do their best to ignore known tags, however every page of yours is compared to others. Plain and simple, clean pages get indexed better. CSS helps you build clean pages. I only bring up one issue. We are still at a point where CSS attributes are dealy with differently from browser to browser, but so are tables. If there is any chance of things getting fixed to be more uniform it would be with the CSS. So start coding your sites that way now and you will be prepared.