problem with different sized divs

This should get things back to normal.

in your html change:

<hr class="floatfixer"/>

to

<div class="floatfixer"/></div>

in your css:

.narrowcolumn {
float:left;
width:600px;
}

.sidebar {
float:left;
margin:0 0 0 30px;
width:180px;
}

The width’s and margin’s will have to be adjusted to compliment the rest of the layout.

Edit: I am not sure why the hr class is not working for you. You would have to find out why that it is happening.