Are you looking for something like this?
Of cause, this would only work if you have a really simple table layout with no rowspan. I'm not 100% sure, but i think with a little effort it would be possible to automate this transformation even for more complex layouts. You could use for example XSL transformations to achieve what you want.
for each (row)
<div class="row" style="height:cell-height">
for each (cell)
<div class="cell" style="width:cell-width/total-width+"%""> (..here Content of current Cell..) </div>
<!-- style -->
But if you just have to rewrite a few documents, then it might be really faster to edit them by hand than to write yourself a transformation algorithm.