The system isn't getting to the kernel, so it can't be a problem with it. The network boot thing is built into the BIOS (Gentoo doesn't have a network install CD that I know of).
The exact ISO was install-x86-minimal-20091103.iso , but the problem is not in the CD, which boots and works just fine. The issue is in the install I made with it, which is being ignored by the BIOS for some reason.
I might try lilo, but I was under the impression it had issues with larger hard drives. Can't hurt, though.
All of these are typed as I don't have any easy way to get the info off the computer, so forgive any typos.
Disk /dev/hda: 30.0 GB, 30005821440 bytes
255 heads, 63 sectors/track, 3648 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk identifier: 0xdd6cdd6c
Device Boot Start End Blocks Id System
/dev/hda1 * 1 5 40131 83 Linux
/dev/hda2 6 3648 29262397+ 5 Extended
/dev/hda5 72 1116 8393931 82 Linux swap / Solaris
/dev/hda6 1117 3648 20338258+ 83 Linux
/dev/hda7 6 71 530113+ 83 Linux
Installed partition fstab:
/dev/hda1 /boot ext2 noauto,noatime 1 2
/dev/hda6 / ext3 noatime 0 1
/dev/hda7 /home ext3 noatime 0 1
/dev/hda5 none swap sw 0 0
/dev/cdrom /mnt/cdrom auto noauto 0 0
shm /dev/shm tmpfs nodev,nosuid,noexec 0 0
(I am aware I somehow swapped my home and root at some point, but that is a minor issue to fix.)