I have a similar problem with a Sony HandyCam DCR-HC40. I'm using a aluminum MacBook Pro (the model from a year ago, before the current unibody form factor), running Mac OS X 10.5.7, and iMovie 09, 08, and HD. Neither Granted Software's Peripheral Vision nor Apple's System Profiler see the camera as connected, and only my built-in iSight shows in iMovie. I've got it connected with an Apple FireWire cable (one of several I've tried from when Macs used to ship with them), and the camera is plugged into AC and set to Play mode before I connect the FireWire.
I wonder if the Sony or FireWire Camera extension/plug-in/framework has been quietly removed in recent OS updates, or disabled by another piece of software (I'm running Parallels, for instance)...