Yeah, the RPM's put it in /opt somewhere. It doesn't install properly with rpm though, because of failed dependencies. You can solve this by adding the --nodeps flag to the rpm command, or even better by rpm2tgz those rpm's before installing with installpkg.

In /path_to_download_dir/OpenOffice.org/RPM/distro-integration there is a slackbuild to put the OOo stuff in your menu's. I don't believe you have to restart X after this, but maybe you do...