How do I set it up so that I can view the cable TV signal on the television set, but NOT have it show up on the monitor? Is there any way to "assign" which screen (monitor or TV) the picture is sent to?
This cannot be done that I know of.
Some of the newer ATI cards (newer than my 7000 series cards) can do multiple monitor output, meant for two computer monitors. I do not believe this function extends to a computer monitor and a tv set.
For something like this, I would have to refer you to rage3d.com forums, or to ATI's 1-800 number. I'm really not all that familiar with this. I have done the multi-monitor setup many times at a friend's home studio, and it's great for NLE work, but not sure about the tv out.
You may want to just experiment. Look at installing the drivers that allow this. I believe they are the HYDRAVISION drivers from ATI.com.