GI SB3100 Cable modem & dhcp

[crash3m]

I'm using @home for my cable modem provider.  We have the SB3100 cable modem 
by General Instruments.  I was reading on the internet that it has a built in 
dhcp server.  The only way I can get this dhcp server to work is by leaving 
the coax unplugged when powering up, then my clients can pick up an ip.  If I 
leave the coax in I can only get 1 IP using my hostname, if I don't specify a 
hostname it will fail.  My question is, is there a way to use the cablemodem 
as a router?  Here is how my current setup is....

cablemodem - gateway - hub - lan

what I would like to do is....

			lan client
                               /
cablemodem - hub - - - lan client
		       			lan client

using the second configuration (without the coax in) all of the clients can 
get a non-routable IP (somehwhere in the 192.168.x.x range) from the cable 
'modem'  

Something else I was considering is using the 2nd configuration, and having a 
single NIC obtain it's IP via 'dhcpcd -h hostname eth0' and also running 
dhcpd to assign the rest of the clients IP addresses.  Is it possible to do 
NAT over a singe NIC?

Matt