OK. I just removed OpenOffice 2.0 from my FC6 install and installed 2.1 from OpenOffice.org according to their instructions. First I removed the RPM for KDE integration from the RPMs directory as I use Gnome. As the OP said, there were no entries in the Gnome menu for O.O.o, even after logging out and back in. In the subdirectory 'desktop-integration' there is an RPM for 'freedesktop-menus' I installed that, logged out and back in and voila! I had my menu entries back!
Edit: Be sure to add 'openoffice.org*' to the 'exclude=' line in /etc/yum.conf or the system will want to update it to the old version again
Edit2: Be in store for more surprises
Previously you had a hidden directory in your /home called '.openoffice.org2.0' where all your settings were stored. Now you'll find another one called '.openoffice.org2' and I suppose your settings were not transferred over.