Having come from Access I am used to creating a field (column) which can be
a "yes\no" or "true\false" but which actually contains "0" or "-1"
Is it possible to do this in excel, and is it possible to have a check box
on the worksheet which will enter the value for me
Just use TRUE/FALSE in the column.
If you pick a checkbox from the controls toolbox, and link that to a cell,
that sets the cell value to TRUE/FALSE.
(there's no email, no snail mail, but somewhere should be gmail in my addy)
And if you you use a checkbox from the Forms toolbar
you can rightclick on it
choose format control
and type in the address of the cell link for that checkbox.
Similar to Bob's suggestion with a checkbox from the Control Toolbox