I have a StreetPilot 2610 with European City Navigator V7 loaded. I now also have Garmin compatible maps of Poland (GPMapa4) installed on my computer, and can alternate between them in Mapsource using the drop down box.
I have managed to download the Polish maps to the card, but of course this then erases the CN maps.
Does this mean that I will have to carry 2 cards (1 with City Navigator maps, and 1 with the GPMapa4 maps) or is there any way I can load both "map families" onto the same card? 
I have managed to download the Polish maps to the card, but of course this then erases the CN maps.

Just downloaded 2 small maps from each family and both now show as separate "Map Families" on the same CF card.