Downloaded intrepid rc iso (64-bit alternate) this morning. Install failed to install grub. This is the same hardware I listed above (I had some spare unallocated disk space).
I don't know what information might be useful for anyone to find out what is going on. I captured a few log files to a thumb drive; if I have one that might be of use I'll post it. Let me know.
Obviously, not many people are having this problem, so it must be pretty unique to my hardware.