Clicking on the “?” button of the DOP Network object or searching for DOP Network and clicking on the result gives the following error:
The file /content/helpcards/obj/dopnet.html cannot be found. Please check the location and try again.

However, searching through the installation, I found this to be the correct path:
hdox/houdini/content/helpcards/obj/obj.dopnet.html

8.1.704 on Windows and 8.1.759 on RHEL4.0.

Cheers!
steven

There is a similar problem with the Null node. I posted it (for the Null) on the mailing list and got a reply from the documentation team that they'll fix it..