Now it may be unnecessary to buy an enclosure at all; I opened up a Western Digital Passport external drive, removed the faulty drive, and popped in the Seagate 160GB hard drive that I had been using in my notebook (but since replaced with a 500GB drive).
My concern is that the Seagate will require more power than the Western Digital--especially since the WD drive enclosed in the Passport shell was jumpered to use RPS (Reduced Power Spinup).
Here (PDF link) are the main specs for the Seagate 160GB drive (model# ST9160310AS):
Power dissipation +5V input average (25° C) Spinup (max) 1.0 amps Seek 1.6 watts Read 2.6 watts Write 2.85 watts Idle, performance* 1.5 watts Idle, active* 0.78 watts Idle, low power mode* 0.725 watts Standby** 0.22 watts Sleep 0.22 watts
Now I'm something of a noob when it comes to basic electronics. I just don't want to shorten the life of a perfectly functional hard drive by putting it in an enclosure that doesn't feed it enough juice. The Passport enclosure may be sufficient for the Seagate ST9160310AS, but then again, it may not. I'd rather spend $6 than take the chance--but I don't know if either of the $6 enclosures are any good, either.
Either external case should be fine. All laptop drives are 5v and will work in an extrenal case powered by the 5v supply from the USB port. I did the same thing with a cheap external case and an Hitachi 500GB drive... All is fine!