I'm fairly sure you can't. The whole idea of DPM 2007 is that it is installed on a dedicated server. Nothing else should be installed on that server. When you have a disaster with the DPM server, the idea is that you just reinstall the OS, install DPM and recover the database.
You could of course always use ntbackup to back up to a file share on another server and back up that file share with DPM.