I"M STUCK! help please!

here is what i want to do:

2 columns: A & B

col A: list of months (12): cell A1:jan/06, A2: feb/06, A3: mar/06, A4:
apr/06, A5:...... A12: dec/06
col B: list of sales that correspond to the month (only 4): B1:100,
B2:112, B3:105, B4:112

I want a formula that will tell me the latest month that the sales is
inputed (in this case B4) = apr/06

i've gotten the formula to find the last number of the set: which give
me the number of "112" (i put this formula in D1)

=INDEX(A1:A12,MATCH(9.99999999999999E+307,B1:B12))

or

=LOOKUP(9.99999999999999E+307,B1:B12)


but where i'm stuck at is using index/match, (i put this formula in E1)

=INDEX($A$1:$A$12,MATCH(D1,$B$1:$B$12,0))


and in the example above, it would always return to me (feb/06) as it
is the same sales figure as apr/06, but I want the formula to to tell
me apr/06!

i've also tried changing the match type to '1' and it did do anything.

i feel i'm so close but cn't figure it out!