I just bought the N810. I wanted to load another Map database, but I get an error saying there is no room. I went out and bought an extra 8gb miniSD card and installed it. I still get the message that there is not enough internal memory. Is there a easy method (which is current to OS2008) that would allow linking of the external map data to the MAP program? If I unload the maps I do not need, will I always be able to download them again when I need them or should I download them now just in case the web site goes away?

Move map directory from internal SD to your new external SD. Map program will pickup from there.
Yes, you can download and save maps in your PC for later use. If you unload mpas you don't need; later on you still can copy/download it again to use them.

You van go to Manage respitories and change the Cache to your external memory card.