I tried posting this as a comment, but couldn't get the columns to display right (as per your question).
You are asking for:
A B
C D
E
... but the answer accepted as the solution will return:
A D
B E
C
... so either the answer is incorrect or the question is.
A very simple solution would be to set the width of your <ul>
and then float and set the width of your <li>
items like so
<ul>
<li>A</li>
<li>B</li>
<li>C</li>
<li>D</li>
<li>E</li>
</ul>
ul{
width:210px;
}
li{
background:green;
float:left;
height:100px;
margin:0 10px 10px 0;
width:100px;
}
li:nth-child(even){
margin-right:0;
}
Example here http://jsfiddle.net/Jayx/Qbz9S/1/
If your question is wrong, then the previous answers apply (with a JS fix for lacking IE support).