I just bought a portable HD (hi speed usb 2.0). I plugged it in and it was immediately recognized but I was unable to write to it or copy data to it. I think it is formated for a PC but the package says it works with Mac OSX. I tried to use disk utilities to format it for the mac but the choice in the field remained grey and I could not do anything with the disk utilities application. Can anyone make a suggestion as to how I can get this thing to work. I have another portable HD that works fine in both my PC and my Mac.