Need guidance installing Drush
If you see Content-Type: text/html when running Drush commands, it means that you are running Drush with php-cgi instead of php-cli.

If you already have php-cli on your system, set the environment variable DRUSH_PHP to point to the full path of php-cli.  If you do not have it installed yet, try installing it and see if that clears up your trouble (sudo apt-get install php5-cli on Ubuntu).