Mirc does support the EUC/SJIS conversion (though that really messes up communication between mirc users that have the option set, and those who don't)
But as long as you are running japanese windows, or, set your default system language to Japanese (under 2k) / Default Language for non Unicode programs (under XP) then it will work fine as it will get all the raw SJIS, and windows will display the characters as appropriate ... unless the person on the other side is running mirc and has the multibyte options turned un, then you will see garbage from that person.
