The Frame, Rules and ColGroup are new additions to tables in HTML 4.0. Netscape 4.x doesn't support any of these new additions, but Netscape 6.x will. This doesn't seem like a critical issue, so I personally would not stress over it to much, but then again I haven't seen your layout either.
What most people currently do to make the center dividing line is one of two things.
1. They make a table for each of the left and right columns and place these within a third table with an appropriate background color and cellspacing to create the effect.
2. Create a cell between the two columns with a background color or a background graphic in it and an non-breaking space to make it show up in Netscape.
you should use 1x1 gif file filled with the desired color. That's how i solved this problem. Put this gif image in empty cell and change the background of the cell to the same color that you used for image file. You probably know what I mean. The point is that this image keeps the width of the cell.