Have you tried adding the following into the <frameset> tag?<br>
cols="240,*"<br>
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This allows the first colum to stay at 240 pixels and the second colum to fill the rest of the page.<br>
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You can do this through frontpage by right clicking on the frame you wish to set, typing in the frame width in pixels under "Frame Size/Width" and making sure the select box is set to "Pixels" and not "Relative" or "Percent."<br>
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Hope this helps.<br>
-Eric