The error isn't from the variable method call, but from using package variables under strict. You'll need to declare $AUTOLOAD with either use vars or our:

use vars '$AUTOLOAD';

sub AUTOLOAD {
   my ($self) = @_;
   my ($method);
   ($method = $AUTOLOAD) =~ s/.*://;
   if ($self->{xmms}->can($method)) {
      $self->{xmms}->$method;
   } else {
      # whatever
   } 
}
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However, in your case, I would avoid using AUTOLOAD and recommend the following:

{
  no strict 'refs';
  for my $method (qw/is_paused is_playing play pause stop/) {
      *$method = sub { $_[0]->{xmms}->$method };
  }
}
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Here, you auto-generate only the methods you want. This way misspelled method calls won't get swallowed up by AUTOLOAD. (i.e, you get the appropriate error message from Perl itself, rather than needing AUTOLOAD to die appropriately).