If A2:A8 consists of 0's, empty cells, and positive numbers:
B2, copied down:
=IF(A2>0,RANK(A2,$A$2:$A$8),"")
The following expensive formula should yield the same ranking as the
foregoing:
=IF(A2>0,SUMPRODUCT(--($A$2:$A$8>A2),--ISNUMBER($A$2:$A$8))+1,"")