well i think everything is clear but i will write again. first do this.
download po and mo from here:
http://glotpress.simple-press.com/projects/simple-press-themes/default/spDefault/no/default
change their name like this:
spDefault-nb_NO.po
spDefault-nb_NO.mo
and put this files into this location:
wp-content/sp-resources/forum-language/sp-themes
and do couple of times F5. goog luck!