dogpile came up with this:
http://www.oreillynet.com/cs/user/view/cs_msg/83976
here is a page that describes what GRUB Error 18 means:
http://wiki.linuxquestions.org/wiki/GRUB#Error_18
Briefly, GRUB Error 18 means "Selected cylinder exceeds
maximum supported by BIOS" and it can be fixed by
"creating a boot partition at the beginning of the disk
that is completely within the first 1023 cylinders of
the harddrive."
in my own case, I find the / "root" partition is 240MB,
with 10 other partitions spread over 3 disks.
perhaps back at the beginning, you have a chance to set
aside a small / "root" partition, putting "usr" and "home" on
others. A few struggles in the beginning, to be expected.