Very simple steps for installation of Zimbra Desktop 2.0 Beta on Fedora Core 13 Beta (soon to be released)
1. sudo yum install xulrunner.i686
Then follow normal instructions for downloading and installing Zimbra Desktop 2.0
If you run into conflicts where versions don't match between x86_64 packages and i686 packages, run:
sudo yum --enablerepo=updates-testing <package>.i686
I had to do this for both openldap.i686 and db4.i686, with the current state of FC13.
Hope this helps someone!