The following intructions are provided by the Winpcap authors

. This version is intended for use on Windows 95, 98, ME, NT, 2000, and XP.

Run the executable.
Follow the instructions on the screen. The installation applet will automatically detect the operating system and install the correct drivers.
The WinPcap-based applications are now ready to work.
To remove winpcap from the system, go to the control-panel, click on "add/remove programs" and then select "WinPcap"

If you have an older version of winpcap on your system and wish to upgrade to the version 3.0 in this directory, remove the old version from the "Add/Remove programs" choice in the control panel, completely shut down your system, and install the new version when the system comes back up.

If you recieve the error "The procedure entry point opterr could not be located in the dynamic link library wpcap.dll", your system has mismatched versions of windump and winpcap. Windump 3.6.2 and older require winpcap 2.3 (available in the archives directory, while Windump 3.8alpha and higher require winpcap 3.0, in this directory.