How to create fluid motion with dynamic variables

Hi, my brian is refusing to work today. I have a very simple problem but cant for the life of me work it out.

I have multiple movieclips on my stage. Im bringing in figures from a xml file which i will used as my movieclip._y positions. So as the figures change in the xml file, my movie clips should hopefully float up and down.

I have assigned them a starting position, bring in the first array of positions and they float there nice. When i bring in their next aray of position they jump back to their first position then float to their second new position???

can anyone point me in the direction of a tutorial or somthing to help me figure this out??