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If you are working in such type of network envoirnment where the IP assignment is set to dynamic then IP Tray can be useful for you. It sits in the system tray and upon mouse hover, it displays the current IP address of your system along with the hostname. You can also copy the IP address information to the clipboard.
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Download IP Trayhttp://www.freelabs.info/iptray.aspx
It works on Windows XP, Windows Vista, Windows 7 and Windows 2003/2008 Server.