Following up, I corrected the menu.lst created during the grub2 installation, substituting (hd0,6) for (hd0,4) and /dev/sda5 for /dev/sda7, and rebooted.
This worked. I linked into the grub2 menu and could choose a kernel to boot. I am hesitant to write this to MBR though, until the initial problem is sorted out.
