You are going to have to set the width (either px or %) in every layer, being as they act like a new web page.
However, I highly discourage that you use layers as they distort on different computer resolutions, I would use tables. They are quite simple to use.
W3Schools Online Web Tutorials is a great site for beginners.
<table> to start the table
<tr>to start a row
<td>to start a column (columns must be within rows)
</td> end column
</tr> end row
</table> to end the table
I would still recommend w3schools. Also you may want to download the trial version of Dreamweaver 8 and see how you like it.