You should check if you have files in /var/cache/apt/archives...

> cd /var/cache/apt/archives
> ls -al tar*.deb

You should see several files listed. If you don't tar wasn't downloaded. Go back and try

> apt-get -d install tar

and answer Y to any questions it asks. Then check the directory again. If you see the tar*.deb files this time, you are good to go and you can continue with the dpkg command.