About a week ago, there was a guest authored post that involved using a script from Matt's Script Archive. I've since been told (quite vehemently by some) that those scripts on Matt's Script Archive are old, buggy, have major security flaws and should be avoided at all costs. (I never used them, so I didn't know)
In any case, there ARE replacements to those scripts, and they can be found here: NMS (Which I think someone said stood for Not Matts Scripts ??).
The post that involved using them has since been taken down. (In case you're wondering the post was about how to make "private" comments in MT – for which there's an even simpler solution than the one in described in the post – which is to show the comments form on your page, but just don't include the code to display the comments.)