GPS Map Software Question

I have the Garmin Oregon 550T and bought the nat geo topo maps for two states. How do I transfer the maps onto my GPS? I have the SD card in and I copy and pasted the maps on the card but cant get them to come up on the GPS? Wyoming for instance has six or so CD's and to view at the 24K level you have to have the disk in the computer?

Any ideas?

Also wondering if anyone knows where to get BLM maps to transfer to GPS?

Thanks