The only way to know for sure about a hard disk is to examine the S.M.A.R.T. logs, and preferably to run a "long" selftest via S.M.A.R.T.

If you can find an Apple or OSX app to do that, then great! Otherwise, boot from a Mac-Linux CD, and run "smartctl -a" and "smartctl -tlong" on the drive.

Cheers