I'm a programmer and recently started running CPDN. Climateprediction.net - a BOINC project.

I'd like to automate backing up CPDN and the first task would be to write code to suspend the CPDN project within BOINC for which I need the API.

Any language would be fine, but Windows only to start. I've started to look at the BOINC API information although what seems easiest to find is how to put your project into BOINC as opposed to manipulating a project that already exists in BOINC.

Pointers, etc would be appreciated.

Have you looked at the README files on the project's alternative board?
There's a section there on Backups, including an automated backup for the old BBC project. (BBC Auto-backup tool)

PS
BOINC needs to be backed up as well, otherwise you lose things like the client_state.xml file. :)