Originaly from Mark Joseph Edwards, Windows & .NET Magazine Security UPDATE
NGSSoftware now offers a free packet-capture and analysis tool called NGSSniff. The tool runs on Windows XP and Win2K using the raw socket capabilities of the OS or the Microsoft Network Monitor drivers. NGSSniff can also import captured packets from files saved using Network Monitor so you don't need to install additional drivers. The GUI-based tool offers packet sorting and ASCII text viewing of packet data and can view packets in realtime without having to first stop a capture operation. NGSSniff is available as a free download from the NGSSoftware Web site.