use a Linksys BEFSR41 cable modem router to make LAN from ADSL Gateway connection?

I'm in the process of switching over from a BB connection via CM from
Ntl to an ADSL connection from UKOnline. I've connected up and
everything works fine to my main PC via the ethernet port on the DSL
Gateway that UKOnline supplied.

I'm now wondering whether it might be possible to use the WAN port on
the Linksys BEFSR41 I've been using with Ntl to distribute the ADSL
connection? If so then I could continue to have a 100Mbps LAN and won't
have to buy any more hardware.

I've tried it - - but the WAN IP the Linksys picks up is that of the
DSL Gateway - there is no routing to the big wide world. Am I hoping for
the impossible or is there something I could tweak?

(As should be obvious from the above, I know little about networking.

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dave @ stejonda