Try this:
string date = "10/14/2012";
int year = Convert.ToInt32(date.Split('/')[2]);
int day = Convert.ToInt32(date.Split('/')[1]);
int month = Convert.ToInt32(date.Split('/')[0]);
DateTime dtOld = new DateTime(year, month, day);
string newDate = dtOld.ToString("dd/MM/yyyy").Replace('-', '/');
Hope it helps!
--Amit