Get a live cd (the gentoo minimal install cd is good) then having got you system up and running:
# mount -t proc none /mnt/gentoo/proc
# mount -o bind /dev /mnt/gentoo/dev
# chroot /mnt/gentoo /bin/bash
>> Regenerating /etc/ld.so.cache...
# source /etc/profile
# export PS1="(chroot) $PS1"
(If you dont use the minimal CD you will need to create these directories)
This chroots you into your gentoo system, and then try
# emerge -D ncurses
You will already have all the source code on your computer, so with any luck this will rebuild ncurses and all of its dependencies.