Hi Nigel,
view
toolbars
customise
commands
catagories = edit
commands : scroll down to the end
select current region
drag the "select current region" icon into your toolbar - it looks like a squashed spider
close
now just click on any cell anywhere which has data in it and then click on your new icon.... it will highlight the full extent of your data, with your down-most row and right-most columns being highlighted