As previously noted, any oversized image or extra long line will cause this problem. Long url's are particularly bad for it. Forced word wrapping on all pages would have to be used. Otherwise, with long url's, you can use the {url=http://your url}your text{/url} syntax. There is nothing the poster can do with large images except resize them before posting. If the image resides on a different web site, this may be impracticle. If the oversized stuff happens to be the most recent post in a particular topic, it can cause the problem on the index page as well if any portion of that post is displayed there.