WinPcap, The Packet Capture and Network Monitoring Library for WindowsPacket library for Windows. WinPcap is the standard tool for link-layer network access in the Windows environments: it can be used to capture and transmit raw network packets and has many useful advanced features, including kernel-level filtering, a network statistics engine and support for remote capture. WinPcap consists of a driver, that extends the operating system to provide low-level network access and a library that developer's can use to easily access the low-level network layers.
http://www.winpcap.org/ 
