public delegate void SendDataEventHandler(object sender,SendDataEventArgs e);

    public class SendDataEventArgs: EventArgs
    {
        private string data;
        public string SendedData
        {
            get { return data; }
        }

        public SendDataEventArgs(string data)
        {
            this.data = data;
        }
    }

//定义一个公共的静态类
    public static class FormEvent
    {
        public static event SendDataEventHandler SendData;

        public static void OnSendData(object sender, SendDataEventArgs e)
        {
            SendData(sender, e);
        }
    }

//Form1中添加对事件的响应

FormEvent.SendData += new SendDataEventHandler(FormEvent_OnSendData);

private void FormEvent_OnSendData(object sender,SendDataEventArgs e)
{
//处理你要做的事
}


//Form2
//在要做事的时候引发事件
                SendDataEventArgs ee = new SendDataEventArgs(str, true);
                FormEvent.OnSendData(this, ee);

------解决方案--------------------
对于窗体的交换，写过两篇文章建议参考，
Windows窗体间的数据交互
http://blog.csdn.net/zhzuo/archive/2004/04/05/22027.aspx
窗体的参数传递
http://blog.csdn.net/zhzuo/archive/2006/05/05/708941.aspx#sec5