Going by your setup, it appears that you are using a cable decoder in order to watch cable TV. Just like hooking up a satellite receiver to any recording device, this means that the cable decoder will have to be tuned to the channel you intend recording. Unfortunately, the only way you would be able to record one cable channel and watch another would be if you use two cable decoders (one for the TV and another for the DVD recorder). Pretty much all digital cable services use a cable decoder. :doh:
Analogue cable TV services that do not require a decoder work just like receiving your transmissions over the air. In this case, your TV and recording equipment tune in the channels directly and there is no other box for cable, thus allowing more than one channel to be watched or recorded at the same time. Most analogue cable services in the US use this approach. NTL's analogue cable service in Dublin is another example. I remember the ads in the early days showing how one could watch several cable TV channels through the house as the main reason to choose cable over satellite. However, this is no longer the case with Digital cable decoders, without the use of a separate decoder for each TV and recording device. :rolleyes:
Finally, I would seriously recommend that you use a SCART or SVHS lead to hook up your cable decoder to the DVD recorder. This gives a much improved picture over tuning the cable decoder over the coaxial lead, especially if you are using a digital cable service.