如何判断Windows断网络(50分)

各位大侠，知道有什么语句或着什么控件能够判断网络连接失败呢，让其连接失败时，弹出对话框？

各位大侠帮个忙

Ping一个服务器的IP地址，若Time Out则断网

我现在要一直监测网络，若网络连接失败，将返回一条信息？
Delphi中有Ping 这个命令？

internetcheckconnection
用这个函数吧。很简单的。不过有缺陷

USES
WinInet;
..
..

function InternetConnected: Boolean;
CONST
// local system uses a modem to connect to the Internet.
INTERNET_CONNECTION_MODEM = 1;
// local system uses a local area network to connect to the Internet.
INTERNET_CONNECTION_LAN = 2;
// local system uses a proxy server to connect to the Internet.
INTERNET_CONNECTION_PROXY = 4;
// local system's modem is busy with a non-Internet connection.
INTERNET_CONNECTION_MODEM_BUSY = 8;

VAR
dwConnectionTypes : DWORD;
BEGIN
dwConnectionTypes :=
INTERNET_CONNECTION_MODEM + INTERNET_CONNECTION_LAN +
INTERNET_CONNECTION_PROXY;
Result := InternetGetConnectedState(@dwConnectionTypes,0);
END;