Well, that 192.168 most likely came from your router. Your ISP gave you 1 ip address, that's most likely the gateway on all your machines when you do an ipconfig /all. But for all the machines to see each other, they have to have a unique ip address, so the router is assigning them in the range of 192.168.1.1 /8, so you can have up to 255 pc's on that network. I would look at the router paperwork to see about adding a new pc, OR just go to the home page of the router mfg; they will give you an ip address to get to the router itself and configure it, and you can most likely find the range of ip addresses that it has assigned. I know on my router (linksys) I open up IE, type in 198.162.1.1, and it takes me to the router, enter in the username/password (admin/admin) and then I can add a new pc from the router itself. I*'m not familiar with that type of router, but that is where I would start.
I rather doubt that your ISP gave you 5 ip addresses; unless you are paying for 5, that is.
