Well, after running the DS Download application on the Wii, I've noticed that the Wii requires dropping the WPA connection to my router in order to connect (with its internal wireless chipset) to the DS via WEP. Plus from what I can tell, the USB adaptor uses windows software to share the internet connection, and not hardware like I assumed.
So I believe using the USB adaptor wouldn't help me much as the Wii wont run the ICS software. It does however beg the question, if I use the USB LAN adaptor (ethernet) for the Wii, /then/ maybe could it act as an AP for the DS? Or is it like the PS3 in that it may only use one chipset at a time eth0/wlan0 ?
I'm getting to the point where if there is a Nintendo designed solution in mind I'd be grateful to hear it, as downgrading to WEP on my network isn't an option, and buying a 2nd AP just for 1 device seems overkill.