Applescript can tell Excel to select a specific range of cells, e.g.
select (range "A1:B20")
and you can copy cells:
copy (range "A1:B20")
However, how can you tell Excel to select all the cells in a worksheet, or to copy all the cells in a worksheet? It seems to require a specific range. However, of course, when you are working with Excel directly you can just press cmd+A to select all.