I think the functionality that you're looking for is the Excel "Fill Down" or "Fill Right" functionality. In Excel, the contents of the "1st" cell are propagated to the remaining selected cells.
I don't think that there are any built-in PB datawindow functions that will do this for you.
You may be able to replicate this functionality in a datawindow by creating a new popup menu option for it that will issue a copy against the contents of the either the left most or upper most "cell", and then paste them to the remaining cells all in one go. You will obviously have to write a script to do this. This will definitely be easier to do for a "Fill Right" than a "Fill Down" (coping a value to other columns on an existing row, as opposed to adding new rows, and copying a value to the same column in new rows.)
Alternatively you could rather than using a PB datawindow, use an OLE control that is linked to an EXcel spreadsheet.
I'd advise you to go with the latter option.
