Did you mean "post comment" section ("Leave a reply")? I see that Firefox 3.5 has no scroll bar, but IE 6 does. I don't have Chrome to try (I should probably snag a copy, just to test pages on). That may just be a quirk of some browsers -- they reserve space for a scroll bar so that if needed in the middle of an entry, it won't reflow the existing text in the textarea. According to my HTML book, "Scroll bars will appear when necessary". I don't see any attributes or CSS to suppress this reserved space, so it may be something you can't do anything about.

I ran the page through the W3C validator and it didn't like it. You have a lot of stuff that's not XHTML Strict, and a bunch of duplicate IDs. Perhaps loosening the doctype to Transitional, or cleaning up the code to Strict standards, might alter the behavior. I don't see any error messages in the vicinity of the <textarea> in question.