All the music scores in the movie were actually performed by the actor and actresses themselves. They were not dubbed.
To promote the movie, the actor and the actresses performed live in concerts in Japan.
Many of the actresses had never played an instrument before. They took intensive music lesson at Yamaha Music School for several months before the shooting began.
With the exception of some well placed character actors, the finale scene of the movie was filmed before a live audience to get their reaction to the band, which due to the last song, turned out to be more than the director had hoped for.
The video game that Tomoko's sister is playing in the house scene is called Space Channel 5 Part 2 for the Playstation 2. The second song the Swing Girls play during the concert is the main theme from the game. The song is called Mexican Flyer by Ken Woodman.