Is Dig not installed on your Ubuntu box? Ask the internets and it'll say: just install dnsutils, easy!
# apt-get install dnsutils
# Package dnsutils is not available, but is referred to by another package....
Not so easy...
Anyway the magic fix is to update your package index:
# apt-get update
You should then be able to run the below as normal:
# apt-get install dnsutils
Now your package index is up to date you can also upgrade all your packages with:
# apt-get upgrade
Also useful to remember, if you end with a broken package, just run:
# apt-get -f install
