Well ... given all the good comments above, one brute force ugly way is:

#/usr/bin/perl

$sentence = "Douglas built five Douglas World Cruisers to attempt his 
+first flight to Buenos Aires. These were the predecesors of the moder
+n AH-64D and AH-64D Apache.";

# split on spaces and some common punctuations
@words = split( /\s+|[.,\/\\;]/, $sentence );

# roll through the words and grab the cap words
# and their position 
$cnt = 0;
foreach( @words ) {
        push( @lol, [ $_, $cnt ] ) if /^[A-Z]/;
        $cnt++;
}

# print out the first match
$prev = $lol[0]->[1]-1;
print $lol[0]->[0];
shift( @lol );

# roll through the rest. print out a new line
# if it's not the next word by count, space if it is
foreach( @lol ) {
        print $prev != $_->[1]-1 ? "\n" : " ";
        print $_->[0];
        $prev = $_->[1];
}
print "\n";
[download]

Like I said ... ugly.

-derby