For input, how about just entering a string consisting of

a row digit of starting position of word
a column digit ditto
either a 'h' or a 'v' for whether the word is horizontal or vertical
the word

Example program:

#!/usr/bin/perl

use strict;
use warnings;

my $board = ('.' x 10 . "\n") x 10;
print "$board\n";

my $input = '23hacross'; # simulated read from STDIN
place($input);
print "$board\n";

$input = '16vdown'; # simulated read from STDIN
place($input);

print "$board\n";

sub place
  {
  my $input = shift;
  my ($row, $column, $direction, $word) = $input =~ /^(\d)(\d)(v|h)(.*
+)/;
  my $position = 11 * $row + $column;
  for ( split //, $word )
    {
    substr $board, $position, 1, $_;
    if( $direction eq 'h' ) 
      {
      $position++;
      }
    else
      {
      $position += 11;
      }
    }
  }
[download]

Outputs:

..........
..........
..........
..........
..........
..........
..........
..........
..........
..........

..........
..........
...across.
..........
..........
..........
..........
..........
..........
..........

..........
......d...
...across.
......w...
......n...
..........
..........
..........
..........
..........
[download]