However, neither of those are as clean as the blockquote method. Blockquotes allowed long lines of text and wide images to fall outside the right margin without affecting the rest of the contained text. Both tables and margins (on a div tag) stretch the right margin to the widest element in the content. This requires horizontal scrolling if the right margin falls outside the width of the browser window. Horizontal scrolling sucks!
I remember running into similar issues when trying to prettify some ebay listings (using Frontpage), and IIRC the solution was to set the left column to a fixed width, and the right column to a percentage of the remaining width. In the FR context there wouldn't need to be the left column (I just note it because it drove me crazy trying to balance the two, prevent the left one (which had the photo) from resizing, and prevent the right column from getting a horiz scrollbar, which as you pointed out, sucks.)
As for the buttons on the reply page, can you use onLoad JS to disable the function of the button until the page is entirely loaded?
I wrote some games and puzzle pages years ago that I had to seriously debug so I know where ya are. Between trying to stick to HTML, JS, CSS, and DOM standards, while trying to handle the idiosyncracies of IE and NS, I had to dig deep into the specs. It was fun :-)
btw, if you don't already have it, I recommend Dynamic HTML - The Definitive Reference from O'Reilly ... great reference book.