It is basically the font you are using. Some fonts use the characters with the high-order bit set (ie. 128 to 255) to make blocky graphics, others use the same characters to show characters from other languages.
Hi!! Thanks for the help, i'm been investigating it: if I use Putty to connect to my MUD, i must to configure it to CP437 font to see the ansi art well. I tried with other fonts but it doesn't works. All the programs to edit ANSI images works with the 437 codepage font, how can i transcode for viewing in Courier font? I have seen that ISO-8859-1/2 Courier font doesn't have the characters that i need to show that ANSI image. Is there a way to configure zMUD to show the MUD with codepage 437? If not, what do you recommends me with de ANSI art?