I wish to enter a formula at the top of a column "Y" that references a column
"X". This formula should be designed to pick off every "n" row of column "X"
and populate every row of column "Y". (n can be defined in the formula, or
in a cell referenced in the formula) I then want to drag the formula down
column "Y" and have it populate every cell the column "Y", referencing every
"n" cell down the column "X".

So, for example, I wish to populate column B with the values of every even
row cell in column A.

Or, the same as above, only poplulate column B with the values of every odd
row cell in column A.

Or, if n=3...

n=3
A B
1 q =A1
2 w =A4
3 e =A7
4 r =A10
5 t =A13
6 y
7 u
8 i