Setting up your device for IP Passthrough is pretty simple:
First download and install Nokia Network Bridge from here
Now when you select 'Ip Passthrough' (when the usb cable is plugged in), the drivers will be automatically installed.
On the E61, create an access point with 'Data bearer' = 'IP Passthrough'.
Connection Name : My Ip passthrough
Data bearer : Ip Passthrough
Homepage : None
The 'Network Bridge' icon appears in the Control Panel, open it and enable the E61 checkbox.
Try to surf/connect and select 'My ip passthrough' as the access point.
Applies to : E61,E70
If you know more devices do update the above list.