1) Looking at the Hard Drive from the connector you will see four pins on the right
2) Buy a JUMPER for these drives (they are very small, prepared for 3.5 drives)
3) Insert the jumper in the extreme right pins (position vertical of the jumper). This is necessary because the Mac Controller only can negotiate 1.5gb, while the drive is 3gb, and although Seagate says that automatically the drive will adjust to a lower speed, this is not true in the MBP mid 2009. Maybe an update of the firmware by Seagate will fix it, and the last firmware is SD 8, which does not resolve this problem.