messagebox.show()
http://msdn.microsoft.com/zh-cn/library/system.windows.forms.messagebox.show%28VS.80%29.aspx
MessageBox.Show("提示信息", "提示", MessageBoxButtons.OK, MessageBoxIcon.Information);
MessageBox.Show("警告信息!", "警告", MessageBoxButtons.OK, MessageBoxIcon.Warning);
MessageBox.Show("错误信息", "错误", MessageBoxButtons.OK, MessageBoxIcon.Error);
if (MessageBox.Show("确定要删除吗?", "询问", MessageBoxButtons.YesNo, MessageBoxIcon.Question) == System.Windows.Forms.DialogResult.Yes)