Ah, I see....that does complicate things a bit. The first thing is to assign a new IP to the router (I think you can do this in the router setup pages), say 192.168.1.2, then disable all DHCP, then manually assign IPs to each computer (192.168.1.3,4,5,6 etc), and DNS servers. The Pipex DNS servers are: 158.43.240.4 and 158.43.240.3....but not sure what would then be the gateway, the router or the modem...?
As far as out of the box goes, the NETGEAR DG834G works pretty well, you can make it "auto configure" the connection as it has built in ADSL modem, and just type in your username / passwd....
Good luck