Hi Angela,

You could set the cell to use Data Validation (see Data|Validation on the
menu). With this, you can even force the input date to fall within a specified
date range - which you could base on the current date if you want to.

For example:
. click Data|Validation|Settings
. Allow = 'Date'
. Data = 'between'
. Start Date = '=DATE(YEAR(TODAY()),1,1)'
. End date = '=TODAY()'
. uncheck 'Ignore blank'
This would force the user to input a date between 1 January this year and
today. Providing your regional settings are in month-day-year form, the user
will have to input the date in MM/DD/YYYY form.

Cheers