C#

UserName.Attributes.Add("onkeypress", string.Format("return next('{0}');", password.ClientID));

private  DataGridViewRow selectedRow;

public DataGridViewRow SelectedRow
{
    get
    {
        return this.selectedRow;
    }
}

this.selectedRow = this.dataGridView1.Rows[e.rowIndex];

if (datagridDialog.ShowDialog() == DialogResult.OK)
{
    this.FillData(datagridDialog.SelectedRow);
}

private void FillData(DataGridViewRow loadedRow)
{
    this.usernameTextBox.Text = loadedRow.Cells["UserName"].Value.ToString();
    etc.
}

public event EventHandler LoadButtonClick
 {
     add
     {
         this.loadButton.Click += value;
     }

     remove
     {
         this.loadButton.Click -= value;
     }
 }

public class FirstDialog : Form
{
    private SearchDialog sd = null;
    ........
    ........
    ........
    ........

using (sd = new SearchDialog())
{
    sd.LoadButtonClick += MyLoadButtonClickHandler;

    if (sd.ShowDialog() == DialogResult.OK) // or whatever
    {
       // do anything required when search closes with OK
       sd.LoadButtonClick -= MyLoadButtonClickHandler;
    }
    else
    {
       // do anything required when search closes with Cancel
       sd.LoadButtonClick -= MyLoadButtonClickHandler;
    }
}

private void MyLoadButtonClickHandler(object sender, EventArgs e)
{
    this.UserNameTextBox.Text = sd.SelectedRow.Cells["UserName"].Value.ToString();
    etc.
}