How should I use div to effectively align content on a page?

I want to use div to align content on my page. Suppose I want to align a menu on the left (20% of the page) and an article on the rest of the space on the right (80% or less). I am currently creating two divisions inside a single div and floating left and right and setting widths in percentages. This method works sometimes and sometimes it doesn't work. Some friends suggest that I should use tables. Should I? I think tables are just a short term solution and don't follow the actual way of coding a page. Is there any other, more efficient, way?