1) On the workgroup member, in explorer navigate to the DPM servers c:\program files\microsoft dpm\dpm\protectionagents\ra\<agentversion>\amd64 (or i386 if installed on a 32bit OS)
2) Run DPMAgentInstaller_x64.exe
Next we need to run the following command which will create a local account to be used by the agent, set security permissions and open required firewall ports for communication to and from the DPM server.
3) Open command prompt and type
cd "c:\Program Files\Microsoft Data Protection Manager\DPM\bin" SetDPMServer.exe -DPMServerName <enter server name> -IsNonDomainServer
-UserName DPMAgent (or whatever you username you choose)
You will be prompted to specify a password for this account. Once done, you should have a message that "Configuration completed successfully!"
Finally, on the DPM server
4) Open the DPM Administrator Console
5) On the Agents tab, under Action, click Install
6) The Protection Agent Installation Wizard will open. Select Attach Agents and Computer in a workgroup or untrusted domain. Next
7) Enter the computer name (or IP address) and the username and password of the account specified in step 3. Next
8) On the Summary screen, click Attach. You should get a 'Success' message.
Thats it! You should now see in the Agents tab that the workgroup member is listed, with the agent status of 'OK'. You can now backup and/or restore onto this server!