The account is locked when anyone enters incorrect info repeatedly. This is for the owner's protection, and can only be reset at Apple.com.
Forgotten passwords are common, but as you might guess, Apple is VERY cautious about resetting passwords, lest they grant access to unauthorized persons!
Follow the link below... there you will find the questions necessary to identify yourself as the rightful owner... just fill out the form, it's quite simple & obvious... then Apple will assist you.
Customer Service - iTunes Store Support
Under "Category" choose "Account or Billing" ... under "Sub-Category" it looks like the 1st choice is the one you want.
Good luck!
~Shadey