With regards to using a "relatively small" (e.g. 2G) card:
Originally Posted by Gino Cerullo
No! Your nüvi probably already has 2GB of storage, and you're approaching that limit already, and maps make up about 85%90% of what is stored on your device.
This assumes that you want to move the entire map from the internal storage to a card. As I've already mentioned, you can split a map between internal storage and a card. In this case, a low capacity card may be sufficient to hold the "overflow". I'm currently using a 1G card.
However, the cost of cards is quite low these days, so paying the extra for a larger card may be worth it for future-proofing.