Can I output my computer's video signal into the cable lines in my house?

"Yes - but it is awkward.

You need to get a graphics card with a coaxial output, however I haven't seen these in years.

Again, I haven't seen VGA to Coax adapters in many years, they simply do not have the resolution and people don't want it!

You are much better off getting splitter boxes and wiring up each tv to them, I know this isn't what you want, but standard coax just isn't really up to what you want it to do."

"how about this?

Grandtec USA GWB-4000 Ultimate Wireless PC to TV Converter:

The Ultimate Wireless is the world's
first truly wireless PC-to-TV
converter. Convert resolutions up to
1600x1200 and transmit the display to
any TV within 100 feet of your PC.

of course this gadget takes care of your audio signal as well!"