The 160GB model is already shipping to retailers and will replace Sony's current 120GB model at the same price of $299.99.
The 320GB PS3, however, will be launched alongside Sony's motion controller PlayStation Move on September 19. It'll initially be available only in a PS Move bundle, though one imagines it'll be sold on its lonesome later.
Announced in July before Sony unveiled the new hard drive size, the $399.99 'PS3 Sports Champions Move bundle' packs a new 320GB PlayStation 3, one PlayStation Move motion controller, a PlayStation Eye camera and a copy of Sports Champions plus a "bonus Blu-ray game demo disc." You'll still need to buy the optional PlayStation Move Navigational controller seperately for $29.99 for the full Move experience, though.