This HowTo will explain how i managed to update the gentoo build environment

Before you update, install the buildroot as described here:
http://www.nas-2000.org/mwiki/index.php?title=Compile_Programs_on_the_NAS

Note: Unpacking the "stage3-armv4l-2005.1.tar.bz2" seems not to be possible
      on the NAS. I used a Live Linux CD with the NAS connected via USB.
      
      This is also a good idea if you want to backup the environment:
      #tar -cjpvf gentoo_buildenv_`date +%Y%m%d`.tbz2 ./gentoo 

BTW: Without updating the build environment it seems not to be possible 
     to install "vim". Installing "ccache" worked for me.

Please be aware updating will take a long time, so i installed "screen"
(see below). Now i can close the ssh connection, shutdown my computer
and reconnect the next morning ;-)


after i installed the buildroot i got this message:

# emerge --sync

 * An update to portage is available. It is _highly_ recommended
 * that you update portage now, before any other packages are updated.
 * Please do so and then update ALL of your configuration files.

i tried to update portage:

# emerge sys-apps/portage
Calculating dependencies \!!! Cannot resolve a virtual package name to an ebuild.
!!! This is a bug, please report it. (virtual/libiconv-0)

i found: http://www.gentoo.org/proj/en/portage/doc/manually-fixing-portage.xml

here is a short version:

# wget -P /usr/portage/distfiles http://distfiles.gentoo.org/distfiles/portage-2.1.1.tar.bz2

# cd /root
# mkdir portage-recover
# cd portage-recover
# tar xfj /usr/portage/distfiles/portage-2.1.1.tar.bz2

# cd /root/portage-recover/portage-2.1.1
# cp -R pym bin /usr/lib/portage/

# rm -f /usr/lib/portage/bin/sed

# emerge --metadata 
!!! Problem with sandbox binary. Disabling...
!!! Problem with sandbox binary. Disabling...
>>> Updating Portage cache:  100%

to fix the sandbox error i tried:
# emerge -av sandbox

success :-)

# emerge -av sys-apps/portage

These are the packages that would be merged, in order:
Calculating dependencies... done!
[blocks B     ] <dev-lang/python-2.3.6-r2 (is blocking app-admin/python-updater-0.2)

i found: http://home.leo.org/~loescher/gentoo.html

# quickpkg =dev-lang/python-2.3.5
 * Building package for python-2.3.5 ...  [ ok ]
 * Packages now in /usr/portage/packages:
 * python-2.3.5: 6.5M

# emerge --nodeps -avt =dev-lang/python-2.4.4-r6
# emerge -pC python
# emerge -aC =dev-lang/python-2.3.5

now compile "screen", this will allow you to reconnect to a session

#USE="-pam" emerge -av screen 
#mount -t devpts none /dev/pts/

the next step will take about 15 hours ...

#screen emerge -avt python-updater

install strace (for tracing)

#screen emerge -avt strace

create "rsync_excludes" again ...

#cd /etc/portage
#touch rsync_excludes
#emerge --sync
 ** Skipping packages. Run 'fixpackages' or set it in FEATURES to fix the
    tbz2's in the packages directory. Note: This can take a very long time.
 * IMPORTANT: 11 config files in '/etc' need updating.
 * See the CONFIGURATION FILES section of the emerge
 * man page to learn how to update config files.

#etc-update

will fix 5 of 11 errors ...
till now i did not try to merge the remaining 6 erros ...

now i can install "vim"

#screen emerge -avt vim