Div width 100% minus fixed amount of pixels

Question

How can I achieve the following structure without using tables or JavaScript? The white borders represent edges of divs and aren\'t relevant to the question.

Answer 1

New way I've just stumbled upon: css calc():

.calculated-width {
    width: -webkit-calc(100% - 100px);
    width:    -moz-calc(100% - 100px);
    width:         calc(100% - 100px);
}​

Source: css width 100% minus 100px