have an hdmi cord? i am thinking about getting the ZuneHD sync dock so i can use it with my computer. i noticed there was an HDMI port on the back. can you get 720p videos through this if you already have an extra HDMI cord laying around that you just plug into the back, or do you have to get the ZuneHD power pack? I already have a usb to wall input converter, so do i still need the power pack?