networking - Mobile broadband sharing over adhoc wireless

I have a Huwaei modem (E1820 to be precise) that i use for my internet whims and fancies. But what I want to do is set up an adhoc wireless network so another device can connect to my network and in turn I want that device to be able connect to the internet through the network. I've managed to set it up relatively effortlessly on Win7 so the it is possible on my hardware. But now I need to do it here.

Basically what i've done is the following.

1. Connect to a "Automatic (PPP)" Mobile Broadband




2. Set up a wireless network

   
   
   
   
   
   1. Set the SSID to a unique name
   
   
   2. Set the Mode to "Ad-hoc"
   
   
   3. Set the IPv4 Method to "Manual"
   
   
   4. Set the IP Address (196.168.137.100), Netmask, Gateway (196.168.137.1) to the same as what I would on win7
   
   
   5. Tried leaving the DNS server blank, tried filling it with the same DNS server the mobile card uses and tried setting it to 8.8.8.8
   
   

tested... didn't work... read some tutorials

1. Installed Firestarter

   
   
   
   
   
   1. Set the Internet Connected Network device to ppp0
   
   
   2. Local network connected device to wlan0
   
   
   3. Enable internet connection sharing
   
   
   

at this point i cant even connect to the internet on this computer unless i disable the wlan

what am i doing wrong?