Sorry if I gave you the wrong impression here - you CAN use both a turbonet card and modem simultaneously, but you have to edit a couple of files manually instead of using nic_config_tivo. Let me know if you want help with this.
To figure out your connection problem, check the log at /var/log/tclient
You may also need to use my hack depending on which ISP you are connecting to.
It sounds like you may have bigger problems to worry about first though.
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