Yes, you will need a special 78 stylus in order to play 78 rpm records on your turntable.  The grooves on a 78 record are wider, so a standard stylus made for 33 or 45 rpm records can damage the 78 record and will sound very noisy.  A 78 stylus can snap right onto the cartridge in place of the standard stylus that came with your turntable.