Question 37499
Good problem.  
I did it by recognizing that they were all powers of two and that exponents add...so we are looking for a standard magic square for the number 0 thru 8, since 1, 2, ..., 256 are the numbers 2^0 thru 2^8...
The numbers are
128, 4, 8
1, 16, 256
32, 64, 2
Each row, column and diagonal's product is 2^12 or 4096.
Good problem.