Solution 1:

Perl, 133 (129) chars

Perl, 167 160 156 147 142 133 D'oh! 147 144 137 134 133 chars

    $_=shift;die grep{5>$n?y/*/#/:y/#*/ |/;$n++-8||y/ /_/}
    @Q=(substr(("*#  #".("*#  #*#   |   #")x2)x9,
    4*/#/+(7&ord)*5,1+/#/+5*pop).$/)x9

Here's a 129 char solution, borrowing several ideas from molf's Ruby solution:

    ($_,$c)=@ARGV;$j=($k=/#/)+ord;
    for$n(0..8){print$/,substr+(join'',map{8-$n?5>$n&&$_%7%4?"###  "
    :" |   ":"_|___"}$j..$j+$c),!$k,-3}

and with help from the Acme::AsciiArtinator:

                sub init_piano{$S=$";$H='#';
                (                            $
               T                              ,$P,$U)=qw(
              T                                          |
             _                                            |
            /                                              )
           ;                                                $
          d             =$T.$H.$S.$S;$t                     =
         $             d               .                   $H
        .              $               d                  . $
       S               .$P.$S.$S.$S.$H;$                t=  $
      d.$H.$t.$t;};$_=shift;-/-/;&init_piano();$Z=/#/;-/|   |
      |                                                 |   |
      |                    YAMAHA                       |  /
      ;die grep{4>$n++?y/T/#/:y/#T/ |/;$n-8||y/ /_/;}@q=(m{
     // // /// // /// // /// // /// // /// // /// // /// /   
    // // /// // /// // /// // /// // /// // /// // /// /
   }                                                   .
   substr(${t}x(9),4*${Z}+(7&ord)*5,1+$Z+5*pop).$/)x(8)
          ;   '                            \   /
           | |                              | |
           /_\                              /';

Solution 2:

Ruby - 125 chars

146 144 140 137 134 126 125 chars

a,n=$*;h=a[1]?0:1;s=a[0]-h+1
9.times{|t|puts (s..s+n.to_i).map{|i|i%7%4<1||t>4?" |   ":"###  "
}.join[h..-4].tr t>7?" ":n,"_"}

(The second newline is not necessary and added only to avoid a scrollbar on SO. Semi-colons can be replaced by newlines if desired.)

The Ruby 1.9 version is different but of equal length (replacing a[0] by a.ord and "_" by ?_):

a,n=$*;h=a[1]?0:1;s=a.ord-h+1
9.times{|t|puts (s..s+n.to_i).map{|i|i%7%4<1||t>4?" |   ":"###  "
}.join[h..-4].tr t>7?" ":n,?_}

Call with

$ ruby piano.rb C 14

Solution 3:

LilyPond, 285 288 291 310 315 330 333 340 350 characters

In keeping with the music theme, here's a solution in a language designed for typesetting music scores, LilyPond:

x=#ly:string-substitute
u=#(x"*""###  ""|   *** |   ** ")t=#(x"###"" | "u)q=#read-char
z=#(q)v=#(if(eq?(q)#\#)1 0)y=#(iota(+(*(read)5)1 v))#(format #t"~{~{~a~}
~}"(map(lambda(s)(map(lambda(i)(string-ref s(modulo(+(*(char->integer z)5)i(* v
4))35)))y))(list u u u u u t t t(x" ""_"t))))

Usage: $ lilypond thisfile.ly <input.in >output.out 2>/dev/null