During normal gameplay on the way to Guru's, if you head to the Namekian Village in the ruins, there's a pushing rock minigame to play there. Beat all eight stages of it, then return to the main game. Hold Up+A and press Start to enter the in-game menu. This will have an extra item in it, "tenrankai" ("exhibition"), letting you access the menu where you view all battle and conversation pictures for all characters and access a sound/music test.