Hi Tony
you've got a couple of options
1) if you're not going to use the numbers in calculations you can format the
cells to text (format / cells / text) BEFORE entering the numbers
2) or type an apostraphe in first (') before the number (e.g. '000123)
3) if you need to use these as "numbers" later on, then make a custom cell
format,
select the cells, choose format / cells / click on custom and type 000000 in
the white line on the right
click OK
Cheers
JulieD