To use xdiff, you will need libxdiff installed, available on the libxdiff homepage http://www.xmailserver.org/xdiff-lib.html.
xdiff is currently available through PECL http://pecl.php.net/package/xdiff.
If PEAR is available on your *nix-like system you can use the pear installer to install the xdiff extension, by the following command: pear -v install xdiff.
You can always download the tar.gz package and install xdiff by hand:
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