This site uses code filter module to diplay code correctly in posts.
use <pre> and <code> tags to wrap your code.
<p>this is a p tag</p>
<h1>this is an h1 tag </h1>
I also put this in my style.css file in this drupal installation:
pre {
overflow-x: auto; /* Use horizontal scroller if needed; for Firefox 2, not needed in Firefox 3 */
white-space: pre-wrap; /* css-3 */
white-space: -moz-pre-wrap !important; /* Mozilla, since 1999 */
white-space: -pre-wrap; /* Opera 4-6 */
white-space: -o-pre-wrap; /* Opera 7 */ /*
width: 99%; */
word-wrap: break-word; /* Internet Explorer 5.5+ */
}