To get a value from a different file, if you know the cell, you would do the
following:
Suppose what you want is in cell B5 on Sheet1 in Book1, the value is:
=[Book1]Sheet1!B5
Also, this can be done by simply typing "=" and then pointing to the value
you wanted from Book1.
Now, this may not be a big help because you may want to look up the values.
In that case it would depend on how the files are set up, whether they're all
set up the same way, and what your lookup values are. If every file is set
up with things in exactly the same position, you could use a sum of formulas
similar to the one above. Since that's unlikely, you will probably need to
use VLookup and still have a sum of VLookups for your formula.