void webBrowser1_DocumentCompleted( object sender, WebBrowserDocumentCompletedEventArgs e )
{
HtmlElementCollection hec = webBrowser1.Document.GetElementsByTagName( "input" );
he1 = hec.GetElementsByName( "radio1" )[ 0 ];
he2 = hec.GetElementsByName( "radio2" )[ 0 ];
he1.Click += new HtmlElementEventHandler( he1_Click );
he2.Click += new HtmlElementEventHandler( he2_Click );
}

void he2_Click( object sender, HtmlElementEventArgs e )
{
textBox1.Text = he2.GetAttribute( "value" );
}

void he1_Click( object sender, HtmlElementEventArgs e )
{
textBox1.Text = he1.GetAttribute( "value" );
}