I don't think that the normal cartridge/stylus combination intended for playing 33 or 45 rpm records will work very well with old 78 rpm records. The reason for this is that the "new" 33/45 rpm records use a microgroove, and older 78's usually don't. There are cartridges with styli that can play both kinds of records, but I don't know how common they are. More info:
http://www.enjoythemusic.com/cartridgehistory.htm