The following works with a closed WB.
=VLOOKUP(B18,'C:\My Documents\Temp\Demo.xls'!MyRange,2,FALSE)
where:
B18 in the open WB holds the item to lookup in the closed WB.
Demo.xls is the closed WB and is located at C:\My Documents\Temp\
MyRange refers to $A$1:$B$10 in Demo.xls.
Or, you can reference the range directly:
=VLOOKUP(B18,'C:\My Documents\Temp\[Demo.xls]Sheet1'!$A$1:$B$10,2,FALSE).
Alternative formula (also works with a closed WB):
=INDEX('C:\MyDocuments\Temp\Demo.xls'!MyRange,MATCH(B18,'C:\Documents\Temp\Demo.xls'!Rng,0),2)
Where the named range “Rng” refers to A1:A10 in Demo.xls.
HTH
Mike