I have one table like this ...
Pk     EmployeeiD      Date        Time
| 1 | Emp1001 | 5/8/2012 | 00:03:02 | 
| 2 | Emp1001 | 5/9/2012 | 00:03:02 | 
| 3 | Emp1001 | 5/10/2012 | 00:00:49 | 
the above values are inserted successfully.....in their respective dates.... 
If a insert the above values again in the same table  means
(ie..)Employeeid        Date            Time
        Emp1001        5/9/2012       00:03:02
it will show some message like (Date Already Exists)....