Not seeing overflow issues with FF2/Win98SE, but that dark blue background makes it tough to read the black text (so something's not allowing the actual bgcolor to display) and there is a syntax error on Line 81:
Code:
dl.menu dt {
background: #0044AA;
color: #FFFFFF;
width: 100%;
align: left;
text-indent: 0;
font-weight: bold;
font-size: 15;
}
(should be "text-align:left;")
Otherwise, in the interest of working with squeaky clean code, you should update your stylesheet with measurement values for many of the entries, for example font-size is specified in a unit of measurement, like 15em or 15pt or 15px, as are width/height/indent measurements. It has been seen many times how an incomplete stylesheet definition can mess up the display in unexpected ways.
As weird as it may sound, fix all of the measurement units in your stylesheet, and see if that fixes your issues.