I need a window's based tool or utility that will take two columns in
excel (or two separate excel files), compare them and spit out only
the differences. Specifically, I have an excel spreadsheet that
contains two lists of different sizes (one list in column A of 200
names, the other list in column B of 500 names).  I want to compare
the two lists and obtain a resultant of only those names that are the
same in the two lists.  Does anyone know how to perform this
comparison in excel or know of a tool or utility that will do this?
Thank You!

one way to do it would be to export them both to ascii (text) or csv files
say list1.txt, and list2.txt.

next, get the "sort" and "diff" utilities from cygwin.com.  these are basically
unix-like utilities you run from the dos-prompt.

then you can perform the following (from a dos prompt) to find the difference 
between the lists:
sort list1.txt > sortedlist1.txt
sort list2.txt > sortedlist2.txt
diff sortedlist1.txt sortedlist2.txt > difflist.txt

also the comments in question 572385 
people talk about a free excel plugin called "duplicate master".
never tried it though.

The 'duplicate master' plugin works great ... it is spot on!! The
cygwin.com was a bit confusing, though the suggestion is much
appreciated. Thank you for your timely response and help. This is a
wonderful service provided by Google. Thank You again!