mIRC is now a Unicode application, which means the characters you print have to be unicode characters. Find the unicode equivalents for your existing script and update it to use those characters.
Note that characters between 128-255, like $chr(196) are no longer font specific. $chr(196) is the unicode codepoint for 'LATIN CAPITAL LETTER A WITH DIAERESIS' (U+00C4), which is why you see that "A" everywhere. The Unicode codepoint for the horizontal line is 'BOX DRAWINGS LIGHT HORIZONTAL' (U+2500) or $chr(9472).
Convert all the respective characters and you will have a working script.
Collective had given you links for this:
http://www.atm.ox.ac.uk/user/iwi/charmap.htmlYou can also find a good list at:
http://jrgraphix.net/research/unicode_blocks.php?block=60