I did see something like this while searching, seems to be the best answer. Luckily it's a script on my site, so i have complete access to the pages. I'll give it a shot and let you know how it turns out.
Originally Posted by
fizzix 
What you can do is have a javascript onload on the body of the forum pages. Use something like this:
function calledOnLoad() {
window.top.getElementById('myiframe').style.height = document.scrollHeight;
}
I didn't test it and some of the properties might be different, but that should give you an idea. Ask me if you have any questions.