My ISP charges 5 bucks for every extra IP I have, so i got a router to use just one IP. If I uplink the ro8uter to a hub, and use two computers hooked up to the hub, will they start charging me for the extra ip addresses?

Hi, If set up properly, your router represents your link to the ISP. Programmed into the router should be an IP address that the ISP uses and from that point on the ISP thinks it is connected to a computer. Assuming that your router only has one port, then you would connect the hub to the router using the uplink port on the hub and connecting it to the port on the router. So no, you shouldn't get charged for an extra IP.

Multiport routers are dirt cheap, I'd sure get one of those and not waste money on both a single port router and hub.

Some ISPs (mostly cable, like ComCast) don't like you to have several internet connected units off one router. They want the $$ for each computer. One of the guys in the shop here had a local Comcast bureaucrat give him a hard time at his home computer because he (our tech)had more than one unit off his router. When he had some config problems he called Comcast tech support and they asked him for his IP number. So without thinking he gave it to him, and the guy saw that it was a router from the first 3 digits of the IP address. After that, about every hour our guy would get pinged off and would have to reconnect. Talk about petty. So he called Linksys and they told him how to configure MAC address cloning and that put forward his computer MAC address instead of the router's and that ended the knock-off problems. So you are warned. ;0)