Sharing Wireless Internet

[CaliforniaBeachUSA]

I need to share wireless internet in my home from my computer to another computer of mine. I know that you can share the internet by being connected to a network through an Ethernet cable and then share that through wireless, but any way to share the internet from a wireless computer to another wireless computer? I have a Wireless Router, WRT54G V5 Linksys 802.1g But my computer (Nintendo Wii) won't use that (don't ask why). So I'm trying to get my Wii to use the internet from my Mac Book Pro.