I also have Cox Cable (in Arizona) without the digital box and it all works fine for me. You shouldn't have to mess with setting the frequencies. Be sure to select 'Cable' in the Tuning: box when you configure your recording source. I think you have the Tuning set to 'Antenna'. In the U.S., the first 15 or 20 channels are the same freq on both antenna and cable but the ones above that are different. That's probably why you're seeing that. Try setting the Tuning to 'Cable'. I think you'll also need the EPG loaded.
Also, you won't get any digital channels without the digital box. With the Cox service I have, the first 99 channels are analog...the ones 100+ are digital and you won't get them without the box (and paying more $).
Sorry, I don't have any more ideas. That works on my system but I'm using two 150MCE's. It could be something weird with the 250. Only other thing I can think of would be to remove & reinstall the latest Hauppauge drivers. I believe they have a pgm on their download site that will remove all their software. Might start with that & then reload only the card drivers. It might be something weird with the WinTV2000 stuff, too. Good luck...