I have a powerbook 167ghz g4, when I plug my new Western Digital 60gig external hard drive in I just get a clicking sound from the drive. It seams to work on other macs. I can't see it in Disk utility.
Is it powered by the USB port (most 2.5" drives are) or an external power supply? If it is, it's probably not getting enough power from the USB port. Try plugging it directly into a port on the machine, or into an independently powered hub.
I think cazabam hit the nail on the head. Probably not getting enough power from the laptop USB port. You could try a powered USB port replicator or get a three-headed USB cable (two ends to connect to the laptop's two USB ports, and one end for the HD). I don't know why it works but apparently that sends enough juice through the cable to power the drive.