Most of the community created iTunes LPs don't work on AppleTV 3.0. This is related to the problem I detailed earlier with the manifest.xml. To fix getting them into iTunes 9.0.2 I suggested you add an almost empty manifest.xml; however it seems that isn't enought for the AppleTV support to work. User phenom posted a comment with some hints to a possible fix. Now I've been able to get something working consistently (thanks to some help by user rob by adding a requirements XML section to the manifest.xml and updating the version identifiers in that manifest, which would result in something like this:

<?xml version="1.0" encoding="UTF-8"?>
<manifest xmlns="http://apple.com/itunes/media_archive/manifest" version="1.0" media_archive_version="2.0">
    <requirements>
        <supported_platforms>
            <platform name="iTunes" minimum_version="9.0"/>
            <platform name="AppleTV" minimum_version="3.0"/>
        </supported_platforms>
    </requirements>
</manifest>

Note that this will only enable syncing and NOT navigating those LPs on the AppleTV. I'm still working out some things about how to get navigation working properly, but I should have something ready for that soon. I'll update the tutorials soon. And I'll try to get to work with the developers of the iTunes LPs on the website now to get those updated and working as well.