HELP: IF with VLOOKUP. Urgent

Sheet 1

A B C AA

1 JR Jan german

2 JJ Jan american

Sheet 2

A B C M

1 Jan Feb DEC

2

3

100 JJ

***What i need the formula in cell b100 to do is: if b1 sheet2 is equal to cell b1 in sheet1, then look for "JJ" a100 of sheet2 in the range of column A of sheet1. If the record is found then give me the value of column AA that corresponds to JJ in sheet1, if not leave blank.

Please help, I have been trying to get this since tuesday. Thank you very much.