Check out page 8 of the Atlas Admin Guide here
To link a background image from the Internet:
1. Click the Home tab, then click Background >Linked Background .
2. Type the URL of the image you want to use, and then click OK.
Regarding the second item, what you can do it create a top level map called UK with a map background of the UK you have. You can then create another map with the background and nodes etc. of the server room. You can then associate the map of the server room with the UK as a child map. A user can then drill from the UK map to the Server Room Map