How setup multi room

I'm not really worried about doing it, i'm more interested how it works out of curiosity. Wen I want to setup 2 boxes in same house I just use 2 user n 2 passwords but I no people do diff. A guy give me a line and told me I can use in as many boxes I want as long as on same up. So how easy is that to do. What I'm more interested in is when he logs on to his web interface and goto active clients or clients does it show only 1 box but shows it using more even or if I have 3 boxes does it show same user name 3 times. I always wanted to no. It's been bugging me lol
Dreamuser