I pressed the wrong button and shrunk the code accidentially. It still should do what you want.

use strict;
use warnings;

print "<text>",join(" ",map{/^(\w+).*?(B-NP|I-NP)?$/;
$a.="<annotation><type>NP</type><text>$1</text></annotation>\n"if$2;$1
+}<DATA>),"<text>\n$a"; 

__DATA__
how B-NP
are
you I-NP
really
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if i my input was this

 how o B-NP
are o I-NP
you o I-NP
some o o
really o B-GP
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and i want the output as <key="type">NP</key><text>how are you</text><key="type">GP</key><text>really</text> That is i want the whole text from B-NP to I-NP to occur in between text open and close tags.

Another change in requirements? Wow. Full rewrite needed for this one.

use strict;
use warnings;
use Text::CSV;

my $csv = Text::CSV->new( { sep_char => "\t" } ); # assuming tab separ
+ated input
open my $words, "<", "words.txt" or die "Cannot open words.txt: $!\n";

# the following shows what's in words.txt; it is NOT words.txt itself!
=head words.txt
how            o                B-NP
are            o                I-NP
you            o                I-NP
some        o                o
really    o                B-GP 
=cut

my $lasttype;
my @text;
while( my $row = $csv->getline( $words ) ) {
        my $text = $$row[0];
        my $type = ( $$row[-1] =~ /\w-(\w+)/ ) ? $1 : "";
        $lasttype = $type unless @text; # special treatment for first 
+row
        if( $type eq $lasttype ) {
                push @text, $text;
        } else {
                print '<key="type">'."$lasttype</key><text>@text</text
+>\n" if $lasttype;
                $lasttype = $type;
                @text = ( $text );
        }
}

# print what's left over when all input read
print '<key="type">'."$lasttype</key><text>@text</text>\n" if $lasttyp
+e;

close $words;
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