In The Groove Cheats & Tips

At the title screen or song selection menu, up in the following code:
Up,Right,UP,Right,Left,Down,Left,Down,Up,Right,Down,Left,Up,Left,Down,Right. Then you get all songs.

For every ten songs in In The Groove that you play, you unlock a new song, or a marathan course, and in some cases, a modifier. Here is how you unlock songs in ITG.

10 Songs: Disconnected ~Hyper Mix~ Song
20 Songs: Bounce Marathon Course
30 Songs: Tell Song
40 Songs: Bumpy Modifier
50 Songs: Anubis Song
60 Songs: Outer World Marathon Course
70 Songs: Bubble Dancer Song
80 Songs: Beat Modifier
90 Songs: Disconnected ~Mobius Mix~ Song
100 Songs: Liquid Moon Song
110 Songs: Don't Promise Me ~Happiness Comes Mix~ Song
120 Songs: Funk Factory Song
130 Songs: Dj Party Song
140 Songs: Tribal Style Song
150 Songs: Infetion Song
160 Songs: The Legend Marathon Course
170 Songs: Pandemonium Song
180 Songs: Incognito Song
190 Songs: Xuxa Song
200 Songs: Wake Up Song