ECI - B Focus 270 -How to configure as router

Hi,
I'm connected to the Internet by ADSL via above-mentioned (Ethernet) "ADSL
modem/router". The default configuration of that unit is as a bridge. I
would like to connect a few PCs (on a LAN) using that ECI unit AS a ROUTER.
I know people have done it.
Can anybody refer me the the relevant (detailed) instructions (I'm using
Linux - Mandriva if that's important although I can also use XP), or, even
better, to the technical manual of the ECI unit?

TIA