xibo needs PHP GD Extension

Installing Xibo (server) on Debian 4.0. During the install.php process when the installer tests the system to make sure everything is in place it tells me:

GD Extension
  - Xibo needs the PHP GD extension to function

All other requirements are met. However, I have installed the php5-gd (version: 5.2.0.8+etch13) through the Synaptic Package Manager, and it still gives me the same message above.

Any help would be greatly appreciated.
Thx
Rob