Apps not seeing Internet

[peregrinef]

I'm not a total Linux newbie, as I've wrestled with Mandrake 8.2 in the past, but decided to try Knoppix 3.7. I'm using a dialup connection through an external modem. It dials in and connects just fine, but when I try Mozilla, just as an example, the response is "unable to resolve host name." The "Details" window shows a spurt of activity at login, then goes flat.

I thought it was a DNS problem, until I tried pinging Yahoo's IP address (68.142.226.44) and got no response -- nothing but lost packets. The "details" window line stayed flat. So, apparently there's a disconnect between the apps and the Internet stack. I'm thinking. I welcome all dissenting opinions, but even more, solutions to the problem.

Thanks in advance.