One way:

=IF(ISNA(MATCH(B46,'07-17-07'!B45:B112, FALSE)),
IF(ISNA(MATCH(B46,'07-10-07'!B45:B112, FALSE)),
VLOOKUP(B46,'07-03-07'!B45:I112, 8, FALSE),
VLOOKUP(B46,'07-10-07'!B45:I112, 8, FALSE)),
VLOOKUP(B46,'07-17-07'!B45:I112,8,FALSE))

In article ,
Janis wrote:

This vlookup works for the sheet its on, but if it doesn't find it I want it
to check the weekending for the 2 previous sheets respectively.

=VLOOKUP(B46,'07-17-07'!B45:I112,8,FALSE)
What I want to know is will this work to nest the if's.
if(=VLOOKUP(B46,'07-17-07'!B45:I112,8,FALSE),=VLOOKUP(B46,'07-10-07'!B45:I112,
8,FALSE),=VLOOKUP(B46,'07-3-07'!B45:I112,8,FALSE))

tia,