I have been working with DPM 2007 and protecting a WSS/MOSS installation. Had to learn the hardway is getting hotfixes and services setup correctly. Some DPM documentations on TechNet did not help much.
Finally here is a good write up on DPM's relationship with WSS 3.0/MOSS 2007. http://sharepoint.microsoft.com/blogs/fromthefield/Lists/Posts/Post.aspx?List=0ce77946%2D1e45%2D4b43%2D8c74%2D21963e64d4e1&ID=69
Still i am dealing with an issue of DPM failing to backup metadata catalog and hence won't be able to perform item level recoveries. (above)