Let me see if I can explain this clearly.

I have a workbook with two sheets. Sheet1 has many, many columns. I
currently have most of them hidden so that only the data I want to use is in
view.

I am opening sheet2 in a new window, so that I can put it side by side with
sheet1. I need to create formulas in sheet2 using the data in sheet1 and I
would like to be able to use my mouse to select the data ranges.

So far everything on screen is set up exactly how I want it...the cells in
sheet2 where my formulas are to go are visible in the top window, and the
data in sheet1 that will be used in the formula ranges are visible in the
bottom window. I should be able to use my mouse to navigate betwwen the two
windows (tabs) to create my formulas...

Here is my problem.

I am in sheet1 and I click the sum button to begin my formula. It
incorrectly guesses what range I want to sum (fine). I delete the range it
guesses from the formula, and then click into my bottom window (sheet1) to
select the correct range to sum. As soon as I click in this window (sheet1),
all of my hidden columns become visable, and my cursor is back at the first
one...WHY? I had the data I needed in the window and the data I didn't need
hidden.

How can I keep excel from unhiding my columns in sheet1 when I go to select
the data range for my formulas?