Can you use a wireless router without hooking it up to a modem? Ok I have an old G router that is not being used because we upgraded to N. My room is on the opposite side of the house from the modem and the N router. Is there anyway I can take the G router and hook it up in my room if there is no modem in the room. My bars are low in my room and I need to boost my connection for Xbox LIVE and video streaming and stuff. Any Ideas?

that would depend on the router, some routers have such capabilities, see if yours have such capabilities.
note that you'll be limited to G though, you can't use N with it.

if you don't know how to connect to your router, http://www.portforward.com/ has information about a lot of routers.

Here's DD-WRT's wiki to setting their router s/w as a Wireless access point. Your router may be similar.

I used DD-WRT in "repeater" configuration to do what you are looking for. It extended the wifi signal to the far end of my parents' house. Works great. google your router and "repeater" to see if it supports something similar, or look into putting 3rd party firmware like dd-wrt or tomato on it if it doesn't.