Sorry for being so short before. As I understood it if it was the HD failing it would have been a DMA 3 error. The site I linked to in my earlier post explains DMA much better than I can.
I still think your HD is ok and if its not an add in card then the Northbridge is about to fail.
I have been wrong before though
once or twice. lol
Hope you can get it fixed. Let us know and good luck.