Derek,
Try entering the following formula in an empty column to the right (or left)
of your data and then fill the formula down the column.
=LOWER(A1)
Once you have filled the formula down the column you would copy the data in
the new column and then do a Paste Special right back onto the new column of
data. In the Paste Special dialog select Values and then click OK. Once you
have the data correctly "cased" in the new column then you can delete the
original column of data.
Note, don't save your workbook until you are satisfied the new data is
correct
Hope this helps.