Hi nqueen,
You could try a combination of the MATCH and AND functions. If you wanted to look up the data on sheet 1 to see if it was on sheet 2, =IF(AND(MATCH(A1,Sheet2!A:A,1),MATCH(E1,Sheet2!D:D,1)),"YES","NO"), then copy this formula into all the rows on Sheet 1.
Hope this if of use.