Find IP Address,DNS Server,or Find the location of a computer

Depending on your System here are the following results:
Windows 2000, XP:
Start/Run:
Enter in the command: cmd
At the command prompt enter in: ipconfig

Vista, WIndows 7:
Go to the command prompt by select the Windows logo and in the search box entering:
cmd
From the command prompt enter in the command: ipconfig

On Windows XP, Vista, Windows 7, if you'd like to know your MAC address (physical hardware address of a your network card), at the command prompt you can enter the following command:
getmac -v

On Mac OS X:
1. Click on the Mac logo on the top left of the screen.
2. Open System Preferences
3. Under Internet and Network, click 'Network'
4. Select which adapter, such as AirPort or Ethernet.
5. Select TCP/IP and you'll see your IP address.. If you receive a dynamic IP address from your internet provider, it will likely be different on your next session. So if you need your IP address for later use, please check when you log on for that session.

The code for it in PHP is the following:
function getRealIpAddr()
{
if (!empty($_SERVER['HTTP_CLIENT_IP'])) //check ip from share internet
{
$ip=$_SERVER['HTTP_CLIENT_IP'];
}
elseif (!empty($_SERVER['HTTP_X_FORWARDED_FOR'])) //to check ip is pass from proxy
{
$ip=$_SERVER['HTTP_X_FORWARDED_FOR'];
}
else
{
$ip=$_SERVER['REMOTE_ADDR'];
}
return $ip;
}

Hope this helps :)