Looks better in a fixed width font :)

[[1,3,1,1,5,1,1,5,1,6,3,5,1,3,1,2,3,2,4,2,1,5,4],
  [1,3,1,1,1,5,1,5,1,5,1,3,1,4,1,3,1,1,1,3,1,1,1,3,1,1,1,5,1,3,1],
  [5,1,4,2,1,5,1,5,1,3,1,4,1,1,1,1,1,1,1,3,1,1,4,2,1,5,1,3,1],
  [1,3,1,1,1,5,1,5,1,5,1,3,1,4,1,1,1,1,1,1,1,3,1,1,1,3,1,1,1,5,1,3,1],
  [1,3,1,1,5,1,5,1,5,2,3,6,1,1,1,3,3,2,1,3,1,1,5,1,4]].each do |line|
   line.each_with_index{|c,i|print((i%2==0 ? '*' : ' ')* c)}
   puts
end


I haven't read through all the solutions yet, so I hope I'm not  
repeating what someone else has done.

Cheers,
Dave