ok so i have had bell south for a long time and finally got sick of losing connection once week cause of bad phone lines. so i switched to comcast. so i took my old linux box i used for bell south and i am trying to get it to work for comcast as a router/fire wall. i am able to access web pages on the the box connected to the cable modem but when i go to any other box on my network all i can do is ping if i try to access the a web page i get sent to comcasts saying please contact customer support. or if i try to use telnet to get the page i get this:
telnet yahoo.com 80
Trying 68.87.64.132...
Connected to yahoo.com (68.87.64.132).
Escape character is '^]'.
GET /
HTTP/1.1 403 Forbidden
Server:ServerIron/9.1
Connection: close
Content-Length: 0

Connection closed by foreign host.

now if i do this on my box connected to the modem i get the html code like i should.

i have the fallowing rules set in iptables:

$iptables -t nat -A PREROUTING -j ACCEPT
$iptables -A FORWARD -i eth0 -o eth1 -m state --state ESTABLISHED,RELATED -j ACCEPT
$iptables - A FORWARD -i eth1 -o eth0 -j ACCEPT
$iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

my modem is connected to eth0 and my lan eth1

i have heard that comcast monitors there traffic for weird mac addresses but i thought masquerade took care of that. could some one please help me out on this please. i would get all my computers back online and scene all comcast tech support would say is we don't support linux or routers there not going to help and i really don't want to switch back to bell south