:)
 thank you frnds.. nw its working... thnk u murali, sanjeeb, Iftikar..

Hi,
        You need to set DataSource as DataTable, not the dataadpter

con.Open();
SqlDataAdapter da = new SqlDataAdapter("select name, age from tblinfo", con);
DataTable dt= new DataTable(); da.Fill(dt);
DataRow dr;
dr= dt.NewRow();
dr.ItemArray= new object[] {0, "-- Select an item--"};
dt.Rows.InsertAt(dr,0);
comboBox1.DataSource = dt;

Regards,
Iftikar

no probs sir.. 
yeah i tried that too..
but there is an error

" Complex DataBinding accepts as a data source either an IList or an IListSource"

my code is:

con.Open();
SqlDataAdapter da = new SqlDataAdapter("select name, age from tblinfo", con);
DataTable dt= new DataTable(); da.Fill(dt);
DataRow dr;
dr= dt.NewRow();
dr.ItemArray= new object[] {0, "-- Select an item--"};
dt.Rows.InsertAt(dr,0);
comboBox1.DataSource = da;

you can go for combobox.

but it is different form asp.net dropdown.

it works like both textbox and dropdown. you can enter your value in this but in asp.net only selection.

its a combination of textbox and dropdown in windows form.

Sorry from my side also.
You need to use ComboBox control.

For which control, you're trying to implement drag and drop behaviour?

It looks like possible in windows controls. 
Exactly what are you trying do here ? 
In which control you're trying to implement this?

Drag-and-Drop Functionality in Windows Forms

thank u sir..

 bt what u saying about drag and drop i cnt get it??

can u explain??

There are lot of difference between windows & web controls.

Web controls:
        Works based on the browser + HTTP Request context etc.

Windows controls
        Depends on the OS
        Runs on top of Windows Forms.
       
When you say, drag & drop, in which control you're trying this?

http://msdn.microsoft.com/en-us/library/ms171546.aspx