I have just had a closer look at your RSS Feed and it looks like a post that the forum admin made was copied and pasted from Word.
Firefox XSLT parser is still able to parse the RSS Feed, but in IE the post that the forum admin posted from Word is coursing IE's XSLT parser to throw a wobbly.
The problem with posting from MS Word is that it also adds in loads of extra gibberish that only MS Word understands, and not only blots the page but courses other issues like this.
There is a 'Post From Word' tool in the WYSIWYG Editor with version 8 that does try and clean up allot of stuff from MS Word, but I would recommend posting from Notepad instead to clean up all the Word rubbish.
Even better, don't use MS Word anymore, use OpenOffice instead from
www.openoffice.org, it's much cleaner, faster, than MS Office and best of all it's FREE and compatible with MS Office Documents.