UDF requires PHP5 and PECL_Gen from the PECL repository. UDF_Gen itself is not (yet?) part of PECL but available independently at http://www.php-groupies.de/php/UDF_Gen-0.2.0.tgz

PECL_Gen and UDF_Gen are both installed using the PECL installer

$ pear -d master_server=pecl.php.net install PECL_Gen 

$ pear install http://www.php-groupies.de/php/UDF_Gen-0.2.0.tgz