Entering a formula depending on criteria of cell

Heres a Puzzles

I know that you can have a cell show any thing if a certain cell conatins data

i.e if B2 had this formula" =(A2="Y","1","0") " then B2 would show a 1 or 0 depending whether A2 had a Y in the cell. This might be incorrect but you get the gist.

Well I have sorting issue, which i have managed to sortout cos i have blanks in the column.

I have now found a way around the problem, but it would be reversing the formula. i.e.

if Cell A2 is populated then enter "formula" in D2 else leave D2 blank

The A column is populated with a ref number when the user enters data into D column
But if nothing is entered into D then there is no ref eneterd into A

Hope this explains stuff

G