hi Divya,
you can use syntax similar to the following in the WHERE clause. your syntax will vary depending on your database...
WHERE
(`table`.`Date`= {?Date} AND '?When} = 'Schedule')
OR
(`table`.`Date`= GetDate() AND {?When} = 'Now')
note that in this command example, there is only one extra parameter...if the end user chooses Now for the ?When parameter, then the above uses the curent date but when when the end user chooses Schedule then the date field uses the data parameter.
-jamie