Share 3G Connection via Ad-Hoc-Network with iPhone

Hi,

I'd like to forward a 3G internet connection via an Ad-Hoc wi-fi to my iPhone. An important detail is that my internal wi-fi is broken and I use a wi-fi USB stick. It's recognized by Mac OS X as a USB ethernet connection and all the wi-fi configuring is done by a configuration utility. I know, it's a little crappy but it serves its purpose...

I use a German Mac OS X, but i think you get the relevant information nonetheless from the screen shots.

This far I already got: I opened up an Ad-Hoc wi-fi network and connected my iPhone with it:

http://dl.getdropbox.com/u/82663/Screen_Shots/Bild%201.png
http://dl.getdropbox.com/u/82663/ScreenShots/IMG0001.PNG

The 3G connection works:

http://dl.getdropbox.com/u/82663/Screen_Shots/Bild%203.png (It says "Connected" (="Verbunden") and "Option 3G Ethernet is currently activated and has the IP address ...")

But I got stuck with the configuration of the USB ethernet connection:

http://dl.getdropbox.com/u/82663/Screen_Shots/Bild%202.png (It says "USB-Ethernet currently has a self assigned IP address and might not be able to connect.")

How do I have to configure the USB ethernet/wi-fi stick settings? I guess, I somehow have to get them in the same network/"IP address area", don't I? I just don't know enough about these things.

Can anyone help?