From Amarok Wiki
If you don't know how to add a repository, you might also have a look at the Kubuntu Community Help, there you can find a step-by-step guide on how to manage the Kubuntu repository list.
Stable version: Amarok 2.1.x
Kubuntu 9.10 the "Karmic Koala" will include Amarok 2.1 as its default Audio player! But for now, packages for Kubuntu 9.04 the "Jaunty Jackalope" are available.
See http://www.kubuntu.org/news/amarok-2.1 for installation/upgrade details for the Kubuntu 9.04 the "Jaunty Jackalope" release.
To enable MP3 support, see MP3 on Kubuntu.