If I have a cable modem and subscribe to digital cable, can I use a splitter and attach my digital cable box so that I can watch TV and and use my cable modem at the same time? Will this degrade the signal? I have Roadrunner.

No. The Cable Modem has it's own connection to the cable box. It's only for the Cable Modem. (At least that's the way mine worked when I had it installed.)

Life is more painless for those who are brainless.

The answer to your question is yes you can use a splitter and yes it does degrade the signal. How much it degrades depends on the quality of the signal to begin with and the quality of the splitter.

I had a long cable run to a TV which I attached a splitter to and connected my modem. many months later i started having issues with my internet connection. After a lot of trouble shooting I found that if I connected the cable directly to the modem instead of going through a splitter it worked fine. The problem was that the signal coming from the cable company had degraded to the point where the additional degradation from the splitter made it unusable for internet.

If at all possible, get the cable company to install two "main" runs from your main junction box - one for internet and one for TV.

Michael J