How come? Take a look at this passage, from the Magarshack version. Here, Raskolnikov's friend Razumikhin has brought him some new clothes. He fits a new cap on Raskolnikov's head, and then:
"Well, now, let's address ourselves to the United States of America, as we used to call it at school. A word of warning, though--I am proud of the trousers!" and he spread out before Raskolnikov a pair of grey summer trousers of light woolen material.
All right, then...fair enough, if a little puzzling. Now read the Pevear/Volokhonsky:
"Well, sir, now let's start on the United Pants of America, as we used to call them in school. I warn you, I'm proud of them," and he displayed before Raskolnikov a pair of gray trousers, made of lightweight summer wool.
Now, you see the difference? The second one is freaking hilarious. And I greatly prefer the word "displayed" to Magarshack's "spread out"...the words are of equal utility, but the Vintage translation seems to emphasize the ridiculousness of the moment--as it's Raskolnikov's last thirty-five rubles, we learn, from which the pants money has been drawn.
I recommend either, of course, but if you're trying Dostoyevsky for the first time, go with the new one. It's very natural, nearly as good as the other great new translation I read recently, Lydia Davis's Swann's Way.