First we must just clarify how the system state backup works. For a windows server 2008 you must install WSB or Windows Server Backup Features before you can make a system state backup with DPM. This is because DPM will use WSB’s function and features to make a system state backup and it’s also the only supported way to make backup of a servers system state. The WSB will dump the backup files to the local disk and the DPM agent will then transfer those files to the DPM server.
To change the path where those files will be manage you must edit the PSDataSourceConfig.XML. The file I located in the C:\program files\Microsoft Data Protection Manager\DPM\Datasources catalogue.
Look for the System Protection part, you’ll see that the default path for system state backup files is C:\windowsImangeBackup. By editing the XML file and change the c:\ to for example X:\ (You’ll need a local drive that has the drive letter X) you will change where the backup files for the system state is placed.