How do you test the transfer rate? Coping a file within the same disc is mostly a combination of reading and writing and slows down the rate. My 60gb tibook drive has around 10mb/s using the same method (copying within the same drive). So, I guess it would be ok for an old 20gb hdd to transfer 4mb/s although current 3.5'' drives can go up to 50mb/s. At least it's not dramatically slow. However, how is the S.M.A.R.T. status of your disk in Disk Utility?