Yet another "feature" from the developers of ubuntu to simplify life. "dos2unix" and "unix2dos" are missing in version 10.04 (Lucid).
First of all, install dos2unix package:
sudo aptitude install tofrodos
Then if you want "dos2unix" type "fromdos" and if you want "unix2dos", type "todos". If you have a habit of typing in the old commands, its best to create links.
Go to /usr/bin:
--->sudo ln -s fromdos dos2unix
---> sudo ln -s todos unix2dos