I have a spreadsheet that users paste reference numbers into from another
system. The numbers are either 4, 5 or 11 digits long. Because a lot of the
11 digit numbers begin with a zero that cannot be dropped the cell format has
to be text.

Whenever the user pastes an 11 digit number beginning in a zero the cell
format in excel gets changed from 'Text' to 'General' and the zero is lost

Any ideas on how I can lock the cell format. Excel 2000 user