802.11b - Linking OS X & WinXP

A friend and I have 802.11b cards in our laptops. He runs OS X, and I run WinXP Pro. I know that we can link our laptops together peer-to-peer/ad-hoc, but we can’t figure out how to share files or an internet connection. Is it possible? Do we need extra software? I’ve tried all the obvious configurations and properties pages.