SmartSniff is a network analysis/diagnostic tool that allows you to capture TCP/IP packets that pass through your network adapter. You can view the captured data as sequence of conversations between clients and servers in ASCII mode (for text-based protocols, like HTTP, SMTP, POP3 and FTP) or as hex dump (for non text-based protocols, like DNS).
On Win2K or above, SmartSniff is able to capture TCP/IP packets using raw sockets. This method has some limitations and problems, but it does not require any additional installation. A better way to capture TCP/IP packets is to install the open-source WinPcap driver (see Dependencies), functional on Windows 98 and later.