The EXIF data is written by the camera (and sometimes it is wrong my Canon 1D mk 11 gets very confused with non canon enses, studio flashes and extension tubes!) this information isn't directly changable in PS, all the other meta data (copyright, locations etc.) attached to the fie is writable in PS. In CS2 the EXIF data is seperatly maintained and labeled as Camera Data 1 and 2 (can't remember if this is different than in PS 7). Photoshop stores all the various formats of meta data in a XMP file, which is the standard format for meta data and can be read by all sorts of different applications.