With a fresh installation of Zabbix 2.0.0 it appears that graphs are not generated. The system values are reported by the installer shows this:

Current value Required
PHP version 5.4.0-3 5.1.6 OK
PHP memory limit 128M 128M OK
PHP post max size 16M 16M OK
PHP upload max filesize 2M 2M OK
PHP max execution time 300 300 OK
PHP max input time 300 300 OK
PHP time zone UTC OK
PHP databases support PostgreSQL
OK
PHP bcmath yes OK
PHP mbstring yes OK
PHP sockets yes OK
PHP GD 2.0 2.0 OK
PHP GD PNG support yes OK
PHP libxml 2.7.8 2.6.15 OK
PHP xmlwriter yes OK
PHP xmlreader yes OK
PHP ctype yes OK
PHP session yes OK
PHP gettext yes OK

Inside php log there have been no warning coming up.