Code:
#faux {
width: 780px;
background-color: #66CC33;
position: relative;
}
#faux #faux-border {
height: 2px;
width: 780px;
position: absolute; bottom: 0;
background-color: #FFFF33;
}
...what? Get rid of that stuff (and associated HTML) for starters.
Also, read about the box model and possibly the IE double margin float bug. Make sure you're doing all your math correctly. Avoid odd numbers for widths.
And don't even test in IE5.5 - it's dead.