Hi,
the whole point of =NOW() and =TODAY() is to provide a date that always
updates. If you suppress the calculation of the spreadsheet these functions
will not update, but neither will anything else.
If you want a date that doesn't update just type it in - 1/22/2009 for
example, or use the shortcuts suggest by Pete which input the Current date or
Current time as indicated by the computer's clock and calendar.
To enter the date and time as hard coded equivalent of NOW in one cell -
press Ctrl+; space Ctrl+: