well, when i made mine i contained a div inside of a div, like so:
Code:
<div style="width: 100px; height: 300px">
<div style="width: 100px; height: 300px; overflow: auto">
--- php here ---
</div></div>
and it works just fine. sometimes though, if there is a broken link inside the posts it'll mess up like you said. i don't know why.

EDIT:

OR you could put the posts into a table inside of a div, with the border set to 0 so its invisible...