Training-bra rock that will be wedged into the family CD player next to the ''Freaky Friday'' soundtrack if you have tweener girls. If not, A Cinderella Story: Original Soundtrack makes a nice coaster. There's a little Mya, a blurt of MXPX, some Edwin McCain, and two slices of ex-Dream Street zygote Jesse McCartney, but this is mostly Hilary Duff's thin, not unpleasant voice spread like cheese over mall-pop arrangements. The duet with sister Haylie on ''Our Lips Are Sealed''? Fine, whatever. Hil singing ''Girl Can Rock''? Uh, no.