Have a look at Win32::Process, it creates processes using the Windows API. A quick test shows that each explorer window shows up as its own process. It also includes a kill method that kills a given process ID.

I'm not sure that Win32::Process ships with ActiveState perl, but ppm shows a couple of versions available.

A quick proof-of-concept follows...

use strict;
use warnings;
use Win32::Process;
use Win32;

sub ErrorReport{
    print Win32::FormatMessage( Win32::GetLastError())
}
my @processes;

for (0, 1) {
    my $tmpPO;
    Win32::Process::Create($tmpPO,
         "F:\\Program Files\\Internet Explorer\\IEXPLORE.EXE",
         "",
         0,
         CREATE_NEW_PROCESS_GROUP,
         "." )|| die ErrorReport();
    
    push @processes, $tmpPO;
    print "Process $_ created: Process ID is ", 
        $processes[$_]->GetProcessID, ".\n";
}
print "Press enter to kill current processes:"; <STDIN>;
$processes[$_]->Kill(0) for (0, 1);
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