The most important key for the DVG is the php_rrdtool extension.

The original can be found at the rrdtool homepage from Tobi Oetiker at the Download Contrib directory.

Unfortuanly the file doesn't compile any more with php 5.3 or later. I've put a fixed copy of the extension on these page. Just download it and following the instructions in the INSTALL File.

If you like to see the diff you can have a look at the viewcvs page.