Start a game in Arcade mode, and set it to the easiest difficulty and one round. 
With any character, press [Hard Kick] repeatedly. You should defeat the CPU 
every time. After you have defeated all CPU opponents with every character, all 
characters except for Akuma and Gouken will be unlocked. To get "Perfects" and 
"Ultra Finishes" easier to unlock Akuma and Gouken, if a round is not going as 
desired, press Start on a second controller.