First of all, install the system. Remember the password you use when you create your own user, we won't make much use of that password, as you will see, but some GUI programs require it to be run with super user-privileges.
Once you are done, log inside and open a terminal, usually typing Alt+T is enough.
Then launch the command sudo visudo, go to the bottom of the file and append the following two lines:
# Allow any user with sudo privileges to launch a command without password prompt
%sudo ALL=(ALL) NOPASSWD:ALL