Things have recently changed in regards to where "new" tires should be installed...
TireRack study.
"Recommendations
Ideally tires should be replaced in complete sets and rotated throughout their life to equalize front-to-rear and side-to-side wear quantity while enhancing each tire’s wear quality. However when tires are replaced in pairs, the new pair of tires should always be installed on the rear axle and the existing worn tires moved to the front."