livecd usr # cd /

Mount the install

livecd ~ # mount /dev/hda3 /mnt/gentoo
livecd ~ # mkdir /mnt/gentoo/boot
livecd ~ # mount /dev/hda1 /mnt/gentoo/boot
livecd ~ # cd /mnt/gentoo

Mount the /proc & /dev file systems, then chroot into your Gentoo environment.

livecd / # mount -t proc proc /mnt/gentoo/proc
livecd / # mount -o bind /dev /mnt/gentoo/dev
livecd / # chroot /mnt/gentoo /bin/bash
livecd / # env-update && source /etc/profile