Galaxys apps running in background

[leemorris1]

Hi All
I have the galaxy portal 2.1 on 3 mobile.
the messages, video player, and music player apps keep running in background, i have task killer which stops them but why are they running in the first place and i can't see where to stop them.

Also i have downloaded and couple of wall paper apps
Where can i set them they down show up anywhere to run just in the manage apps section.

thanks
Lee