Very slow operation and data transfer is a well known HD failure mode.
I just sent a 160gig SATA2 drive back to Seagate for this very reason.
They sent me a new drive with NO questions asked.
Over the years I've replaced dozens of HD's for this same problem.
Check the warranty status of that drive. If it's still in warranty, you might just get a new one.
Cheers Mate!
The Shadow
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A person with experience is never at the mercy of a person with an argument.