I’m no html expert, but my WordPress blog also had the problem of displaying <!–[endif]–> in the body of posts and losing the sidebar in Internet Explorer. (Firefox and Safari are fine.) I solved it by editing each problematic post in WordPress using html. Wherever I found code beginning with:
<!–[if gte mso 9]><xml> <w:WordDocument>
and ending with
<!–[endif]–>
I deleted it. This makes the post look normal in IE. Once you have fixed every post on the page, the sidebar returns.
How ironic that two of Microsoft’s competitors, Mozilla and Apple, have no trouble dealing with the code from Word, but Microsoft’s own browser can’t handle it.