How to find Total hours?

Question

i'm new to SQL ecpeialy on DATE related operation

In my table  starttime and  endtime two columns are there, i need to find sum of total hours group by employeename.
how can i do this?

 exm:  EmpName            Starttime                   EndTime
          A         14/2/2012 25:20:00   14/2/2012 25:20:00
          A         15/2/2012 20:20:00   15/2/2012 25:20:00

But i need output as
                 EmpName TotalHours
                      A          20:25:32(eg)
please help.............