Joe:
You need to let us know exactly what model of "StreetPilot" you have. If it is one of the very early models, such as the black and white one, or the "StreetPilot Colormap", then the answer is no, you cannot use any CityNavigator or CitySelect product, because those two units don't support serial number unlocking of the maps. They are so old (literally, from the last century), they were produced before serial number unlocking of maps was invented.
This means you are limited to the MetroGuide family of maps, if you want current map data. But, think carefully before going out and buying new cartography - you might find that the memory capacity of those older units (32 megs max, I think) renders them unusable for anything other than just navigating around within about 50 miles of your house (assuming you don't live in a big urban area, such as London).
PanEuropean