The rule is this – a “de” attached to a single-syllable name stays no matter what. Anything longer, and removal of the honorific means removal of the “de”.
So you read de Gaulle’s books, but you peruse Tocqueville’s works – and Villepin’s, as the minister is also an author.
And “de”, by the way, is NEVER capitalised.
Just for the record, the new prime minister‘s full name is Dominique Marie François René Galouzeau de Villepin. (It took me years to fully absorb the idea that Dominique could be a man’s name; when I was a kid I was quite confused by the Singing Nun‘s “Dominique, nique, nique” and its references to “he.”)