Why your code doesn't work

If all the machines have their C-Drive shared as c$ (and that's a big if, but I don't know your network, and then it's Windows' default sharename anyway), then you will have to escape the $, as in

The rest doesn't need to be escaped.

Ways to improve your code

Using the same approach, but more clean code:

my %paths = ('KaZaA Lite' => 'c$/Program Files/KaZaA Lite/kazaa.exe',
             'KaZaA' => 'c$/Program Files/Kazaa/kazaa.exe');

foreach (@machine) {
    foreach my $key (keys %paths) {
        print "Bah! Someone installed $key on $_!\n"
            if (-e "//$_/$key");
    }
}
[download]

Now, you can scan for additional files very easily, without changing too much of your code (only the hash at the beginning, actually).

Different approaches

You might consider running a portscan against these machines, focusing on ports that are known to be used by p2p software. Yes, it's not failsafe, but it helps. Most users will not bother to customize their install, I guess.

You might also consider scanning the whole network share for suspicious file names, in case the user installs the program in a non-standard location.