Prompting for database connection

Add a COM reference to:
Microsoft OLE DB Service Component 1.0 Type Library
Microsoft ActiveX Data Objects 2.7 // any 2.5 or higher version is fine

You can then write code like:

//
// Prompt for a totally new connection string
//
private void button1_Click(object sender, EventArgs e)
{
    bool Cancelled = false;
    string ConnectionString = string.Empty;

    MSDASC.DataLinks d = new MSDASC.DataLinks();
    d.hWnd = (int)this.Handle;
    ADODB._Connection c = (ADODB._Connection)d.PromptNew();
    if (c == null)
        Cancelled = true;
    else
    {
        Cancelled = false;
        ConnectionString = c.ConnectionString;
    }
}

//
// Edit a connection string
//
private void button2_Click(object sender, EventArgs e)
{
    bool Saved = false;
    string ConnectionString = "Provider=SQLOLEDB.1;Integrated
Security=SSPI;Persist Security Info=False;User ID=sa;Initial
Catalog=Northwind;Data Source=.";

    MSDASC.DataLinks d = new MSDASC.DataLinks();
    d.hWnd = (int)this.Handle;
    object c = new ADODB.Connection();
    ((ADODB._Connection)c).ConnectionString = ConnectionString;
    Saved = d.PromptEdit(ref c);
    if (Saved)
    {
        ConnectionString = ((ADODB._Connection)c).
          ConnectionString;
    }
}