someone on here requested this, be aware tho I may possibly have errors here as this I already configured a while back on my 8800nl.
1 - login to the gui and make sure in advanced mode.
2 - Click WAN in menu
3 - Click edit next to the WAN service
4 - Change type to bridging, vlan id 101, click apply.
5 - click LAN in menu
6 - click interface grouping in menu
7 - tick groups isolation box
8 - click add
9 - on add page name the group name Bridge, move the ptm wan interface to the right, move also one of the lan ports to the right, the port you have the ethernet cable in that connects to your router's wan port. Then click apply.
10 - should now work as a modem with your router handling ppp/dhcp.
See my other guide, if you want to only use one cable shared for stats and WAN.http://forum.kitz.co.uk/index.php/topic,14621.msg273308.html#msg273308