i recommend using style sheets for the basic font formatting.
anything where you are using columns, i would recommend using a table. if you really like to use CSS, then just keep your tables to a minimum and only use it for your column layout.
if you can somehow cut that top graphic into 2 sections, then you could make the top scaleable to however wide (or thin) the user's computer is. the left side of the graphic would need to fade to a solid blue, or something that can tile. the right graphic would need to fade from that solid tile into whatever you want justified to the right.
here's an example of how the header might look, along with the columns of the nav/content, and the footer.
HTML Code:
<body>
<!-- here's the header -->
<table border=0 cellspacing=0 cellpadding=0 width=100%>
<tr>
<td width=400><img src=images/top-left.jpg width=400></td>
<td background=images/bg-tile.jpg> </td>
<td align=right width=200><img src=images/top-right.jpg width=200></td>
</tr>
</table>
<!-- now for the content -->
<table border=0 cellspacing=0 cellpadding=0 width=100%>
<tr>
<td width=150 align=top> here is my left bar</td>
<td valign=top> here is my content>
</tr>
</table>
<!-- bottom bar to stretch allt he way across -->
<table border=0 cellspacing=0 cellpadding=0 width=100%>
<tr>
<td align=center> my bottom bar </td>
</tr>
</table>
all this formatting would be supported across browsers, .. and you could go to town with the CSS on most everything else.