Pasting a layer to the same spot it was copied from, HOW?

Not sure I understand your question. But if you mean you are making a selection in one layer than want to paste that selection on a seperate layer in the same position as the first:
1) Make the selection
2) Copy it (ctrl C)
3) Create new layer and leave the selection active in the first layer
4) Shft+Ctrl+V (paste into).

What if I need to cut a selection and paste it into a new layer in the same position?

Thanks.

Got it....

make selection
ctrl c
del
shift ctrl v
then apply layer mask

sorted..

An addition to the above methods...
If the Anti-aliased box is checked before the selection, after the cut selection is pasted into a new layer I noticed a thin border of background around the composite picture. Unchecking Anti-aliased eliminates this problem. (This applies only to the the Elliptical Marquee tool or Lasso tools. The Rectangular Marquee tool does not have the Anti-aliased option)