Eliminating data in set that is not in other set

Hi all,

I have two sets of data, which both start with a column of unique identifiers. The first set of data is a subset of the second set - the first set has about 3000 rows; the second set has 99,500 rows. All the entries that are in the first set are also in the second set - with identical identifiers.
What I would like to do: The first set of data has information that the second set hasn't, and vice versa. So I want to merge these two sets, while getting rid of the 96,500 rows that are not in the first set (i.e. 99,500 - 3000 = 96,500). What is the easiest way to do this in excel? I attached an image that uses a small example of the problem. Thanks!

Screen shot 2012-06-18 at 12.44.07 .png

I made a workbook explaining the problem. Could you maybe show how you could use vlookup to do this automatically?
Thanks!

https://dl.dropbox.com/u/8114735/exp...20problem.xlsx

Awesome, thanks!