Do you need to buy another SD card, or will the Topo map fit on the 64meg one which is supplied with the unit?
The way I got Topo it was supplied pre-installed on a new, bigger card from MapsWarehouse
Website here
I didn't buy the Mapsource program as it's unlikely I'll ever use the GPSr outside the area I live in - if you do you will need a new microSD card.