The canonical way of doing keyboard remapping under X is by xmodmap. I did try this method for polish ISO8859-2 characters, and had many problems. Here is my usenet thread about it: input of iso8859-2 characters. I don't remember it too well, but to add to it I remember that the KDE2 own method did not work, and the only way to go with KDE2 was with the xmodmap.