i need code in c# for dropdown , by selecting anyone data i need to display the data in the grid ,that data have to retrive from the sql server 2005

For a dropdown box in C# you will need to use a ComboBox control.
In the combobox SelectedIndex changed event handler you will need to retrieve the selected value, then rebind the datagridview with the relevant details.

Check out this tutorial or google for C# SQL to find plenty of details on retrieving the data.