I have a column (say Column A) with 300 values (basically it is a DDE link
with data I update).

I also have a cell I would like to use (say B1). In cell B1 I would like to
be able to enter a value (say 20) where I will be able to use this value in
another cell to "observe" the top 20 of the cell from column A. So, If I put
20 in cell B1, in cell (say C1) I would like to put some formula where it can
reference the "how many observation" cell B1, and say sum A1:AXX where xx is
the value in cell B1.

I know in this form it cannot be done, but was wondering if someone had an
idea how to get this concept to work,

Thank you for your time.
Diane