Wal Mart has a 90 day in store return policy on video game consoles, such as Xbox 360, PS3, Wii, PSP, DS Lite. Everything that was in the box when purchased is required, even if it has been used. The receipt is also required for a cash refund. (or refunded in whichever way you paid for it)
..but sometimes (if no receipt) you may get lucky depending on the condition of the system and what you "decide" to tell the customer service clerk (if they fall for it).. They will require to see your ID/Driver's License and provide you with a gift card.
PS. If they say NO, then ask to speak with an assistant manager.. sometimes they are easier than the regular associates or CSM.
If the assistant manager says NO, then you are screwed!!