A floated sidebar, contains a table. No problems there, as the sidebar container has a (pixel-) defined width. A main contents area, with a red border (static <div>, width defined only by margins and padding).
The tables should be as wide as the main contents, and not drop under the sidebar.
a table, no width is declared; without a wrapper [control table]
| cell1 | cell2 | cell3 | cell4 |
| Lorem ipsum dolor sit amet, consectetuer adipiscing elit. | Aliquam ultricies, metus sed rutrum dignissim, leo dui sollicitudin sapien, | sit amet sagittis est metus ut erat. | Maecenas sollicitudin. Lorem ipsum dolor sit amet, consectetuer adipiscing elit. |
a table, width declared (100%); equally sized cells; within a wrapper (height:1% and width:100%)
| cell1 | cell2 | cell3 | cell4 |
| Lorem ipsum dolor sit amet, consectetuer adipiscing elit. | Aliquam ultricies, metus sed rutrum dignissim, leo dui sollicitudin sapien, | sit amet sagittis est metus ut erat. | Maecenas sollicitudin. Lorem ipsum dolor sit amet, consectetuer adipiscing elit. |