tar is a *nix utility.
I'm willing to bet you are sitting there in windows with WinZip trying to untar this archive. That won't work in a million years.
For arguements sake, WinAce will extract the files for you in windows, but even still they will be useless to you. 1. cause you won't be able to compile em and 2. cause even if you had a compiler those files are written for *nix and won't compile properly anyways.
What you need to do is find a win32 binary for ettercap.
Ok, so I decided to find one for you. Problem is that they don't officially exist.
from ettercap README.BINARIES:
Ettercap is distributed officially ONLY in source code. Binary packages in ANY
form are NOT officially supported. Although it is not prohibited to distribute
binary packages, the authors will not respond on bugs found in them. If you
use one of these packages downloaded from Internet, redirect your bug report
to /dev/null. The authors will reply to bug reports and will be happy to find
a solution only for hand compiled executables. Every Linux distribution, but
even *BSD or Windows is different from another. What is compiled on my machine
may not work on yours because of a different version of a system library. To
avoid this type of missing dependencies, we will not distribute any binary for
any operating system. Most of the popular distributions (Debian, RedHat,
FreeBSD, OpenBSD, ecc) provide the binary packages for ettercap. Use these
packages, since they are build to work on your distribution and should have
the dependencies resolved correctly. Refer to the binary packager of your
distribution for problems regarding these packages.
So it looks like you either find a compiler for windows and compile it yourself, or install some flavor of *nix on something and do it there.