Yep, Beauxbatons and Durmstrang are mixed.<em>Goblet</em>had Beauxbatons bringing both genders to the tournament (hardcover, U.S. edition: pp. 243 ["A boy in pale blue robes"], 244 ["about a dozen boys and girls"]).  Durmstrang's less obvious, but on p. 257 it states "said one of the other Durmstrang boys" (implying that not all the students were boys) and p. 258 states "The boy with food all down his front nudged the girl next to him and pointed openly at Harry's forehead."  Since the Durmstrang students were traveling in a pack, presumably the nameless girl went there too.<br/><br/>A quick skim shows that only the word "students" is used for both schools before and after those points (except of course for Victor and Fleur).