Mine is a slightly different method than the others, a kind of 'c' like solution. I'm personally fond of the use of 'split' above, myself.

#!/usr/bin/perl
use warnings;
use strict;
while(<DATA>) {
    chomp;
    next unless ( m/(\.|\,|\?)$/ );
    my $len = length($_);
    my $pos = index(lc($_), " it ");
    if ( $pos > -1 ) {
        my $delta = $len - $pos - 4;
        my $string = substr($_,$pos + 4,$delta);
        print "Substring = $string\n";
    }
}

__DATA__
Tim created the Module List in August 1994 and maintained it manually 
+till April 1996.
By that time Andreas had implemented the Perl Authors Upload Server (P
+AUSE) and it was happily feeding modules through to the CPAN archive 
+sites.
Since PAUSE held a database of module information which could be maint
+ained by module authors it made sense for the module listing part of 
+the Module List to be built from that database.
[download]

And I may have reformatted the text, but my output looks like:

C:\Code>perl substring.pl
Substring = manually till April 1996.
Substring = was happily feeding modules through to the CPAN archive si
+tes.
Substring = made sense for the module listing part of the Module List 
+to be built from that database.
[download]

Update: fixed the case sensitivity issue.