I assume you are using fireworks created tables?
If so, my answer is; Don't!
To retain your menu bar and not have it create gaps, it needs to be contained within it's own table.
A basic table layout I use (if I have to use tables, CSS is often better)
Outer table, with 3 rows and 3 collums.
Join first row so you have a colspan of 3 - this is for the header/ title
set width of first collum 2nd row to the width you want the menu to be.
Put self contained menu table into this cell.
join bottom row 3 collums, (colspan again) and use this as a footer.
join the two centre rows collums (the ones that don't have the menu) if you want, or leave them seperate, but assign widths to them, or you will have issues.
pictorially, you start with
row1 col1 | col2 | col3
row2 col1 | col2 | col3
row3 col1 | col2 | col3
and end up with
row1 colspan3 (header)
row2 col1(menu) | colspan2(content)(or two set width cols)
row3 colspan3 (footer)
Hope that helps.
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Sometimes, when my code just won't behave, I take it outside and make it listen to britney spears music, and when it comes back it's really well behaved. I wonder if it's suffering from post tramatic stress syndrome now..