NTL Business with Cisco 871 Router

[lhunt]

All,

I have been trying to configure my new Cisco router with NTL Business Broadband. I have spoken to the NTL helpdesk and they say as long as I can connect to their service with a direct PC to modem connection, the service is working fine. With the router i am using the Cisco SDM software to configure it. At the moment i am getting an IP address from the modem on the WAN port on the router (using DHCP of course). However when I connect to internet on one of my machines it says connecting to page and takes ages to get there if it gets there at all. My firewall and NAT are enabled. I can ping an address form the router with an 80% success rate. Why is this not 100%?

If you require any further details ask away!!

Thanks in Advance

P.S I have an NTL Business 2020 Modem. I have tried the config page and it doesn't have many options other than change user password.