First of all, nl isn't Greek. You want el. Specifically, you probably want language-support-el, which brings in fonts and other stuff for Greek.
Second, Intrepid is probably EOL, so it's no longer in the main archive. If that's the case, you have to edit /etc/apt/sources.list and replace archive.ubuntu.com with old-releases.ubuntu.com and apt-get update with this new address before you install anything else. If you are using a mirror, XX.archive.ubuntu.com, you have to replace the entire XX.archive.ubuntu.com with old-releases.ubuntu.com, dropping XX.
Try this and tell me if it gets you anywhere.