Could someone recommend the exact model I need to get to replace my slow 320 GB 5400 RPM hard drive with the fastest 7200 500 GB hard drive I can get? A link to Newegg or some mfg part/model number would be appreciated. Thanks!!! - M P.S. How difficult is it to replace the hard drive myself? I have a time machine backup so I should be ok from that point of view.