Hi there,
The info sheet on the 7k160 hds721616pla380 Hard drive was dated Aug 2006, so I'd be surprised if it is still under warranty.
You can call Hitachi in San Jose at 888 426-5214 for specific information
This is a standard desktop SATA 3Gb/s drive and you can purchase new 1 TB SATA drives for around $79 now. Just a thought.