How to share internet among 2 android devices?

I have in my possession a G1 and a new Android tablet (the Kmart one, the Gentouch). The Gentouch uses wifi to access the internet; the G1 uses a T-Mobile cellular connection. Ideally, I'd like to somehow cause that G1 to emit a wifi access point, so that whenever the G1 and the Gentouch are in close proximity, the Gentouch can piggyback off the G1's internet connection and reach the internet itself. Assuming I am willing/able to root both devices if necessary, how would I accomplish such a task?