I do the same here, the scart goes into the freeview/sky/video/dvd out (whatever device you want to play through your speakers) some have a in-out switch on the scart cable which you would set to out and put in the tv instead. Then the white and red cables go into the AUX in at the back of the stereo. If you are going from a different box (not the TV) then you will need to plug the yellow into the TV Video in aux.
If you need any spare parts check http://www.everythinglink.com