# download and extract german language pack
http://drupal-de.googlecode.com/files/de.po.zip

# enable locale module
Administer > Site building >Modules
admin/build/modules
check: Locale

# install german language
Administer > Site building > Translate interface > Import
admin/build/translate/import
Language file: de.po/de.po
Import into: German 
[Import]

# set german to default language
Administer > Site configuration > Languages
admin/settings/language
German: Default


# Links
http://drupal.org/project/de