How to set a 'div' height same with his neighbor?

You could do this

<div class="wrapper">
    <div class="dynamic">
        Dynamic Line <br />
        Dynamic Line <br />      
        Dynamic Line <br />
        Dynamic Line <br />      
        Dynamic Line <br />
        Dynamic Line <br />      
        Dynamic Line <br />
        Dynamic Line <br />      
    </div>
    <div class="static">
        Static<br />
        Static<br />        
    </div>
</div>

CSS

.wrapper {
    position: relative;
    width: 400px;
    overflow: auto;
}

.dynamic {
    position: relative;
    background-color: yellow;
    width: 200px;
}

.static {
    position: absolute;    
    background-color: orange;
    width: 200px;
    float: left;
    left: 200px;
    top: 0px;
    bottom: 0px;
    right: 0px;
}

I think jQuery is the best solution to achieve this. Check out my fiddle:

http://jsfiddle.net/PHjtJ/

$(document).ready(function() {

    var dynamic = $('.dynamic');
    var static = $('.static');

    static.height(dynamic.height());

});