I\'m about to begin working on a web page with a complex table-based layout (coded years ago).
One of the things I\'d like to do is convert the layout to a proper CS
There generally isn't a silver bullet in converting between table and CSS. Every site is different and has different requirements. The only real answer is: simply start the markup from scratch.
The best advice is to write the markup entirely first. Make sure the markup is accurate, semantic, and represents your data entirely. Do not write the stylesheet... yet. After the markup is done, create the CSS. This way you have semantic markup and CSS is purely controlling the presentation.
CSS frameworks often don't advocate this approach to semantic markup because they force you to add additional tags to comply with their approach. Consequently, CSS frameworks are sometimes more trouble than its worth.
Do the markup, then the CSS.