Dealing with fluidity

[MrApples]

I've been having trouble making my header fluid. I gave a table column 100% width so that it would take up the remaining space, this worked before, but now it's crushing the rest. I'm assuming the width="100%" is taking priority over the rest of the tables whose width setting is in CSS.

I've decided the best option would be to calculate the remaining width with JavaScript. (correct me if i'm wrong please) So would this work?

<img width="getfiller()" src=blah... />

In JS file...
function getfiller(){
    var a = getelementbyID('td1').width;
    var x = screen.width/100 * 99 - a;
    // ( 99% of Width of Screen) minus Width of Others
    return x
}

Don't pick on syntax stuff please, except should return have a " ; "?