I'm not sure the best way to do this. I have 2 workbooks (I can easily
combine them in one worksheet-that is not the problem). In the first I
have a column of identifiers and corresponding data in the adjacent
column. In a second workbook I have a list of identifiers, which
includes all the identifiers present in the first workbook, and a
column of data associated with them. After I combine them into a
single worksheet I want to look up the data value associated with the
same identifier and move it next to the first set of data. For example:

1A 1M Convert to 1 A M
3B 2N 3 B O
5C 3O 5 C Q
4P
5Q

The real files are much larger and the identifiers are not listed in
order. In Walkenbach's Excel 2003 Bible Chapter 12 page 256, it
suggests using Index and Match functions as such:

=INDEX(F2:F21,MATCH(B1,D2:D21,0))

But this would only return the corelate for the identifier in B1. Can
one somehow drag down this formula in a column B so that all B1:B2000
is matched or can one replace B1 with an array? or is there some other
way to do this?
Thanks,
Dennis