Lookup function - Wrong info when I add lines to reference spreads
 

I have a series of numbers in one spreadsheet and the number that I put a "X"
next to, I want to bring it into my existing spreadsheet. Here is the
formula I am using:
=LOOKUP("x",'[PW Bid Tracking.xls]Contacts'!$G$73:$G$77,'[PW Bid
Tracking.xls]Contacts'!$F$73:$F$77).
The problem is that when I add lines to the spreadsheet it is looking up the
formula from, the formula looks up the wrong cell.
Is there a way to update the fomula automatically so that when I add lines
to the spreadsheet, it still looks up the information that i want it to?