This depends on who the ISP is.  If it is USWest, then they don't need to know
the MAC address for the nic as the IP is assigned to the DSL router (provided he
got the external 675, instead of the internal 605 which doesn't work with
linux).  The dsl router then acts as a DHCP server for all the boxes on the
network.  Even before the switch over from bridging to ppp mode, USWest didn't
need to know the MAC address.  I had a WinNT box hooked up initially and then
put a linux box up to act as a firewall, they had different NICs, but USWest had
no problem with the change.

> I had quite a few problems with DSL in Linux, so I hope I may be able to
> help now that it's working. There are a couple of things you need to make
> sure to get the connection going.
> 
> 1. Ensure that the correct NIC driver is being used and assigned to to the
> correct ethernet device. (most likely eth0).
> 
> 2. Make sure your ISP has your MAC Address registered for your NIC. You
> can find your MAC address by using ifconfig(in Red Hat...not sure about
> Caldera) or by running winipcfg from Windows on the same machine. Call
> your ISP and make sure they have it registered.
> 
> 3. Make sure you have DHCPCD installed and running.

-- 
"Intel giveth and Microsoft Taketh Away" - Gordon Moore