I have the same type of hard drive for my 90BT, I think I am running into the power issue most have described on here because I notived the HD was not spinning up even though the light came on.
My question is regarding the format. My WD Passport does not have the Fat16/32 file format...instead it has EXFAT. I was doing some research and I know that the Windows CE 6 will recognize EXFAT, but My Avic is Windows CE 5, and I couldn't find anything that tells me whether or not it will recognize that file system.