Using my Macbook as the access point for the Nintendo DS

Here's the setup: fiber optic modem, non-wireless router, Macbook, Nintendo DS. The Macbook is hooked to the internet through an ethernet cable. I'm wanting to share the internet with my DS through the Macbook.

I've set up internet sharing through the sharing preference, with sharing from ethernet on the Macbook to computers using AirPort. On the Network preference, the Airport option is on, but with a self-assigned IP address. The DS can find the Mac, but can't connect. Has anyone been able to connect using this method or do I have to do something else to get my DS to connect?

Thanks!