I've always heard the S pronounced in Athos, Porthos, and Aramis.
D'Artagnan - typically pronounced as Dart an yan. In French the apostrophe signals a slight pause.
Planchet - Is pronounced exactly like it's spelled Plan chet
Grimaud - Gree mode
Mousqueton - Moosk tawn
Bazin - Baz een
Milady de Winter - is also exactly like it's spelled
Cardinal Richelieu - Reesh loo
Comte de Rochefort:
Comte - the beginning is like starting to say the word computer but with a T at the end. COMPT.
de - The second part is kind of hard to describe, I can't think of an equivalent in English maybe someone can help me out with that. It's kind of like say duh, only really short. Where an american would draw out the U sound, in French it's clipped and very short. Ah! When you say your ABC's? Say de like you would pronounce the letter D.
Rochefort - Roesh fort (the first syllable has a long o, like Oprah)
Louis - Loo ee the fourteenth of France
M. de Treville:
M - stands for Madame and is pronounced like it's spelled, the E is silent.
de - same as before
Treville - sorry, I don't know how to do the accent grave (which is the little mark over the E) but it's pronounced
Tray veel
Constance Bonaceiux - Bawn ah sew (?)
Monsier Bonaceiux - Muh see yer Bawn ah sew
(I'm sketchy on the last name for those two)
Queen Anne of Austria is as spelled
George Villiers:
George - Make an almost Z sound for the first G and then pronounce the second G like J.
Villiers - Vill ee yers
Does that help?