I have a garmin nuvi 2000. I bought the 2009 map update(CD). To my disappointement, there wasn't enough space on the Garmin to accpet it. I have an SD card from my camera, but it still says I don't have enough space.
Map updates usually override the maps in the internal memory. You could however use the SD card slot to add maps of a region (not already covered) on the device.
Assume you mean North America City Navigator. It will not fit on a 1GB SD card. If you have a 2GB SD card it should work. 2GB SD card is pretty chap these days. If you do not want to use a card, you can just load most but not all of the map. To do this, in Mapinstall when it comes up with the full North America Map, drag to select all, then use ctrl-leftmouseclick to Un-select some stuff like maybe Alaska, Hawaii and Canada for example, then write the map to your 1GB SD card or your Nuvi200.