Just locked your PCI-E to 100MHz will do 

-pWs-

overclock won't kill da harddisk...

Tapirus, you've been warned..do hard-modding at your own risk..any hard modding project, you better consider first if you can accept accidentally frying something.. 
Overclocking won't kill your HDD directly, but possible for it to kill it indirectly. If your PSU can't handle the overclocking and blows up, it can also take out some of your hardware. Theoretically, its impossible to kill a hard disk via the data lines as long as the power is stable, but I had a similar experience to yours which left me confounded-I was using a reliable PSU (which rules out the PSU blowing up scenario) and I was trying to find my max overclock when I forgot to turn down the HT multiplier, after that windows got corrupted and then the hard disk would experience errors every now and then, enough to make windows crash consistently at boot after about a week or 2 or usage. I checked the hard disk and it turned out to be suffering from read errors, fortunately almost all of my data could still be copied out. Sent the HDD directly back to seagate for RMA and got back a replacement unit a few days later, by then I bought another HDD and sold the Seagate to verz84.

I'm completely at a loss to describe how that HDD failed, it was never allowed to overheat and until the overclocking incident it had passed all HDD tests with no problems. The only explaination that I found reasonable is that is happened by sheer coincidence, after all hard disks fail eventually, some earlier and some later.