SilverStripe by default sends templates as suppperrr strict XHTML (which some people like, some don't) but this means it complains about every little detail. By the looks of the error hamish provided you are missing a </div> in the template
@Michelle - keep asking those questions! I learn a lot from reading other peoples' responses too.
@Will - it's great that SS almost always validates as XHTML strict (if not, it's usually because of a templating issue), but might be worth reminding people, especially if you're working with (say) IE7 that hides the errors.
There is another downside - I've reported a bug where random characters are appended to the beginning of the stream. IE7 handles it, but it breaks FF3 because it's not correct XML. Until that's fixed, I'll make a point of validating the site, then switch strict XML off.