The archive footage is drawn from over 60 years (the dates of the earliest snippets are hard to ascertain), but includes bits of interviews from several members of his family, not to mention the man himself. There were also clips from various members of his casts and crews, including Angela Lansbury, Charlton Heston and Gloria Swanson.
There are also numerous clips from the films themselves. Many of these seemed to have been colour tinted at some stage, which was a little strange when those parts of the film are only in black and white in the DVDs in my possession. Most notably the parting of the Red Sea scene from DeMille's first Ten Commandments. The sea itself was tinted blue, whereas the Israelite's reaction scenes where sepia. I'm not sure whether this is simply a different print, or something TCM did themselves, but I did kind of like it. As there are already two versions of the 1923 film (with and without a coloured exodus scene), I wouldn't been surprised if this was original, but then the colour did seem rather bold, and I don't recall reading of DeMille colour tinting before in spite of him pioneering with technicolour.
Anyway I found a few interesting new revelations and watching this overview of DeMille's life in one swoop gives a more immediate perspective than reading a more detailed version (like Birchard's) over a longer time period.
Incidentally you can see a trailer for this documentary from the site previewing it's appearance at 2007's San Francisco International Film Festival.