"So I assume your Mac uses WiFi ....."
That's often the main problem isn't it, posters provide almost no information to enable people to help?
Anyway Jake, try this:
Go to the dock, open System pref's -> Sharing, setup the boxes as in my attached pic'. I'm posting this reply via that configuration, on a macbook, running 10.7.5
HTH

- sharing.jpg (44.07 KiB) Viewed 846 times