Why don't you use tables instead of DIVs?
Tables are easy, you can set the width to a percentage of the totall width of the table....
Let's say you want 3 columns...then the widths would be 33%, 34% and 33%......4 columns is even easier...simple 25%
Example (3 columns) i use on my website:
<table border="0" width="100%" cellpadding="10">
<tr>
<td width="33%" valign="top">
everything you want to appear in column 1 goes here
</td>
<td width="34%" valign="top">
everything for column 2 inhere...
</td>
<td width="33%" valign="top">
everything for column 3 here...
</td>
</tr>
</table>
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