To align your forums to the left you need to put the entire forum in a table.

To do this, add the following code to the very top of your header template
Code:
<table width="$stylevar[outertablewidth]" cellpadding="0" cellspacing="0" border="0" align="left">
<tr>
<td>
and this code to the very end of your footer template
Code:
</td>
</tr>
</table>