Comment on Install Google Sitemap Generator beta1 on Debian x86_64 Lenny GNU/Linux by chris thomas.
I figured it out. you need to create the directories:
mkdir /usr/local/google-sitemap-generator/conf
mkdir /usr/local/google-sitemap-generator/conf/etc
mkdir usr/local/google-sitemap-generator/conf/etc/apache2
then make a file called: apache2.conf by doing this:
touch /usr/local/google-sitemap-generator/conf/etc/apache2/apache2.conf
Then rerun the script and it will work.