Drive Genius shows a problem

I'm about to upgrade to Snow Leopard from 10.4.11. I ran Drive Genius to see if my internal drive needed repairs. DG says "repair failed: overlapped extents found. (extent 348670 overlaps extent 348669 by 979 blocks)". Then I ran Apple Hardware Test, which found no problems. I've searched Apple Support for enlightenment but found nothing useful.

Can anyone tell me if I have a serious problem here? Should I proceed with the new OS install? I have a SuperDuper bootable copy of the drive that supposedly has a problem. If I have installation issues, will this extents thing leave me screwed?

Thanks for whatever help you can give.