On Mac OS 9 you just need to add the fonts to the Fonts folder in the System Folder.
Are these definitely OS 9-compatible fonts? If you double-click the font on OS 9, does it show a sample of the text? If it doesn't, then it can't be used on OS 9. You might need to use a program on OS X to convert it to the correct format for OS 9.
Having problems adding fonts to Os 9 Mac Classic on iBook G4 running OS X. Have tried using Font Book to transfer individual fonts and also folders to OS 9 Classic. After transfer the new fonts are added to the menu in Font Book, bit after opening Os 9 Classic programs, none of the new fonts show in the font selection menus. Also tried adding fonts to the fonts folder in OS 9 System folder.