I dunno, this is the first time i heard of someone worrying about unstable hard drives while overclocking. I think you should be concerned about your CPU & RAM as thats what gets unstable when overclocking the CPU. To check for stability use Intel Burn Test, for Intel 775 CPUs (and i7 also, i think), Orthos, Prime 95 and OCCT. Do a CPU and RAM blend stress test or check components individually. For RAM also use MemTest.
There are utilities that check the health of the hard drives though they dont get unstable while overclocking, at least not to my knowledge. You can use HD Tune to test your HDDs. Also, almost every major drive manufacturer has their own utilities to test hard drives. Go to your drive manufacturer's site and download the approriate tools, i recomend the DOS based myself.