cut & paste group photo

hi - I'm not a graphics person,
but have been using PSP 5.x for years to touch up photos, edit pixels, etc..

I now have the classic situation of a group photo for my son's swim team,
and there was one person "out" that day.... hence, not in the photo.
I have a head/bust shot of him, and would like to place him into the group 
photo.

I can't seem to get it right playing with layers.
All I want is the selection from the head shot - cut out -
and then placed "behind" the rest of the folks in the group shot...
like a 
real world cut & paste.
I can get the cut out using the freehand tool,
but don't know how to totally place the selection "behind" the group 
photo....
What am I missing here.... go slow with the layers, as I'm stumbling enough 
:)