I too have a problem with kppp. I would like to get it working. I can use kppp to dial up. It will connect. But that's all. No surfing, no nada.
In the meantime, I have found an alternative. As root, I ran /usr/bin/neat and set up a connection with the same info that I plugged into kppp, and yet here it worked. Root can use this interface to make or break a dialup connection, but only root. If you want to start and stop this connection as Joe User, use /usr/bin/redhat-control-network. Both of these items can be found in the redhat menu, the first under SystemSettings/Network and the second under SystemTools/NetworkDeviceControl.