Unlock all Default Songs & Mickey Chorus Leader
From the Main Menu, access the Password & Puzzle Gallery section. Enter the following code on the D-Pad at the password screen (the one with all the question mark icons):
Left, Up, Down, Right, Left, Down, Up, Right.

This will unlock 20 songs and Mickey as the Chorus Leader.

Unlock all Default Songs and Disco Magic
From the Main Menu, access the Password & Puzzle Gallery section. Enter the following code on the D-Pad at the password screen (the one with all the question mark icons):
Up, Up, Right, Left, Down, Up, Left, Right

This will unlock 20 songs and Disco Magic.

Unlock All 22 Songs
Finally, to unlock each and every song in Dance Dance Revolution: Disney's Dancing Museum, do the following. From the Main Menu, access the Password & Puzzle Gallery section. Enter the following code on the D-Pad at the password screen (the one with all the question mark icons):
Up, Left, Right, Down, Up, Right, Left, Down

This will unlock all default and secret tracks