Lasrix just buy another 80gb drive identical to the one you already have and then RAID 0 them. That will be a lot cheaper and a lot faster than just buying a newer hard drive. Make sure to back up all your data though as you have to reformat and start fresh with the RAID setup.
I have two 80gb drives in RAID 0 myself and they are faster than my 10,000 rpm raptor which cost the same price as the both of them.