I am not a good CSS knowing person, but can suggest one solution. You may make one large div with position absolute and lowest z-index and margin-left:210px, the cover it with another to div's: left and right with greater z-index and same position type, set for right div something like: right:0px. Did not tested, so sorry if it will not work.
BTW, tables is not so bad thing. For cells better to use table, for boxes div. Its different tags for different purposes. Not wise to try to replace them with each other.