Asking for help again.

Not sure how to go about this but I have read different articles in this
forum and on the web but still cant get this sussed.

I have a sheet "Input" which I want to use for entering prices. it has
data is in column D
Customer name - selected via validation list
Customer No - uses lookup
Currency - uses lookup
Product - selected via validation list
price - input by user

I have the code that will copy the cells to another sheet (Data).

What I want to do is before that data is copied check to see if the Customer
and Product already exists.

If it exists need a msgbox to appear "customer and product combination
already exist. Price is (use value from the Data sheet column E) Do you wish
to replace.

If the user says yes then copy over existing record on Data sheet.
if the user says no then clear cells and exit sub.

I am using excel 2003.

Is this possible?

Thank you
Winnie