Networking/wireless internet question- not really sure what to do

I'm not completely sure what exactly I'm asking here and have never done anything with any kind of networking/ wireless internet, so bear with me please. I plan to build a high-end gaming rig. I want it to be able to access the internet. The internet in my house right now is AT&T DSL(i think). We have a 2wire box that is plugged into our main computer. I plan to put the new computer in my room-quite a ways from the other computer, so I can't run another cable to it. What do I need to make sure my computer has internet? Also, will i need a network card? Thanks for the help, and if you need clarification, please post. I'll try to explain what i know.