Hello Bill,
It depends on the player and what features it has. For instance, Archos installation for the "Player/Studio" model (mono charcell screen, no radio, no recording) takes up only 850KB while the istallation for the iRiver H300 (which has colour screen, radio, recording, more plugins etc.) requires 4MB of space.
Notice that there is also a fonts pack (which is supplied seperately) which can take about 6MB (for all 60 fonts) but of course the user can install only the fonts that want to use.