Wirelessly posted (iPhone: Mozilla/5.0 (iPhone; U; CPU iPhone OS 2_2 like Mac OS X; en-us) AppleWebKit/525.18.1 (KHTML, like Gecko) Version/3.1.1 Mobile/5G77 Safari/525.20)
If I were trying to serve 3 floors with it, I'd do one of two things:
1) Get a wireless router and put it on the middle floor or
2) still get a router for the first floor and try its range out then, if I need to extend the network to reach the third floor, purchase a second router to do so.
Hope this helps.