Drush not being found although installed [ubuntu 11.04]
Your problem is probably that Drush is not in your $PATH.  I did not try to install Drush-4.4 from Synaptic to test whether or not this is the case; instead, I would recommend that you install Drush via PEAR following the instructions on the Drush project page.  If you do this, your $PATH will be set, Drush will be found, and better yet, you'll be able to use the much-improved Drush-5.1 instead of the out-of-date Drush-4.4.

Edit: By "Dash Home", do you mean that you are trying to type "drush" into the Unity Heads-Up Display?  If so, instead run "terminal" from HUD, and then type "drush status" from the terminal prompt.  Then you should be good to go.  I'd still recommend installing 5.1 via PEAR.