You can use INDIRECT to do this, but the other file must be open at the
same time. Try this:

=VLOOKUP(A5,INDIRECT("'["&A1&".xls]Sheet 1'!$A$1:$Z$10"),2,FALSE)

I'm not sure why you have a range 26 columns wide when you are only
bringing data from the second column.

Hope this helps.

Pete