IceShooter isn't far off --most NICs can read whether or not you are using cross-over or not, and can self-adapt for your purpose. If your NIC is less than, say, five years old, most likely you have nothing to worry about with what kind of cord you have.
I'm going to guess that you are using WinXP, but other OSs (even Linux) usually have something about "bridging" connections, which is probably exactly what you want. First you make sure both networks (your wireless to the "host" computer, and the P2P network for the one you want to connect to the wireless). Afterwards, look at the information (it might be as simple as right clicking) on the wireless connection about Bridging that connection. It should be fairly straight-forward, but you can also find other information on it if you look.