Actually, I found a better one for IE: ieHTTPHeaders.

Install now. Then, when you lose a post, it's basically the same thing as with Firefox and LiveHTTPHeaders, except you turn on ieHTTPHeaders with View->Explorer Bar->ieHTTPHeaders.

So, you get the "the BBS has eaten your post" message. Click back. Click View->Explorer Bar->ieHTTPHeaders. Click forward. IE will tell you that the page has expired. Click reload. IE will prompt you that it has to repost the data. Tell it to do that. Look in the ieHTTPHeaders window and find your text. It'll be in the first transaction. Select the text and click Ctrl-C to copy it. Click back again. Paste your text in the box, and click Submit again. Done and done.