1. Demo 1
  2. Demo 2
  3. Demo 3
  4. Demo 4

The wrapper and "mainContent" create new block formatting contexts in IE only.

The DIV that wraps the 3 columns below is styled as follow:

.wrapper {
  width:740px;
  background-image:url(faux-column.gif);
  background-repeat:repeat-y;
}

clearfix is applied to "mainContent"

Heading

.mainContent {
  padding-right:200px;
  padding-left:200px;
}
.floatMe {
  float:left;
  background:teal;
  color:#fff;
}

Screenshots

browser families
screenshot of Demo 3