The reason for so many switches is because, the top one is in a different room where i sometimes had more than 1 computer connected. Didn't feel like running an extra cable to that loction. The gigabit switch in the middle should be fairly obvious. The router WRT54 is wireless, I would of gotten an access point at the time but this was cheaper. And the modem can handle more than 1 ip address.
http://broadband.motorola.com/noflash/sb5100.html