One of my buddies in Texas, Jason Buffington is a product manger in the Storage Server group and is a DPM guru!
Jason did a FANTASTIC screencast around of Data Protection Manager and how it really works. The screencast is about 10 minutes long and trust me, it is time well spent. He talks about the secret sauce behind DPM and how it works down at the block level of the hard drives.
Check it out here:
How does DPM really protect data?
I have spoken with Jason in the past on TechNet Radio. Jason and I just got done recording another interview for the next version of DPM. Check back here around Sept. 12th for the links to hear the interview. We talk about some great new solutions in DPM!
[UPDATE!!] You can check out the radio interview here: TechNet Radio Interview --- System Center Data Protection Manager 2007