Best Way to do Columns in HTML/CSS

I would suggest you to either use <table> or CSS.

CSS is preferred for being more flexible. An example would be:

<!-- of course, you should move the inline CSS style to your stylesheet -->
<!-- main container, width = 70% of page, centered -->
<div id="contentBox" style="margin:0px auto; width:70%">

 <!-- columns divs, float left, no margin so there is no space between column, width=1/3 -->
    <div id="column1" style="float:left; margin:0; width:33%;">
     CONTENT
    </div>

    <div id="column2" style="float:left; margin:0;width:33%;">
     CONTENT
    </div>

    <div id="column3" style="float:left; margin:0;width:33%">
     CONTENT
    </div>
</div>

jsFiddle: http://jsfiddle.net/ndhqM/

Using float:left would make 3 columns stick to each other, coming in from left inside the centered div "content box".

You should probably consider using css3 for this though it does include the use of vendor prefixes.

I've knocked up a quick fiddle to demo but the crux is this.

<style>
.3col
{
    -webkit-column-count: 3;
    -webkit-column-gap: 10px;
    -moz-column-count: 3;
    -moz-column-gap: 10px;
    column-count:3;
    column-gap:10px;
}
</style>
<div class="3col">
<p>col1</p>
<p>col2</p>
<p>col3</p>
</div>

In addition to the 3 floated column structure (which I would suggest as well), you have to insert a clearfix to prevent layoutproblems with elements after the columncontainer (keep the columncontainer in the flow, so to speak...).

<div id="contentBox" class="clearfix">
....
</div>

CSS:

.clearfix { zoom: 1; }
.clearfix:before, .clearfix:after { content: "\0020"; display: block; height: 0; overflow: hidden; }
.clearfix:after { clear: both; }