I'm creating invoices using Excel 2003 (Office Pro) in Windows XP SP2

My summary spreadhseet contains names in Column O (Alphabetic "O")

For duplicate values in Column "O" of my summary spreadsheet, I need to
create a new Invoice (spreadsheet) based on duplicate Values in column "O".

I know enough to sort first by Column "O" on the summary spreadsheet, and I
know how to add new spreadsheets, but I don't know how to generate a new
spreadsheet based on a change in the value in column "O".

Example names from Column "O"

Smith John
Brown Harry
Green Rita Mae

Can someone provide some ideas for this?
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Thank you so much for your help!