electricpete,
True enough, you don't NEED an add-in - but ask yourself, which is REALLY easier and more efficient:
a) Write a VBA macro.
b) Go to a suitable blank cell; select "Insert | Function | Text | Lower", point to the first cell to be converted and click "OK". (Alternatively, just type in "=LOWER(CellReference)".) Now drag to create a full array of the data which is to be converted to lower case. This creates a copy of the whole range of data at a new location, concerted to lower case.
c) Download ASAP Utilities. Select a range of cells, select "ASAP Utilities | Text | Convert lowercase" and click "OK" - this converts the selected range in-situ - no duplication.
Just my $0.02 worth. Given that it's free, and gives you some 300 useful functions, why not try it?
(And no, in case you are wondering - I am not on commission - just a convert to a great free utility!)