I have co-ax cable run through my whole house, so I can watch in
almost any room what is playing on the VCR in my bedroom. It works
great. Can I now do the same thing with either RCA or S-video cables?

Yes to both. However, there are some potential (minor pun there!)
problems that can arise due to ground loops if you connect devices
together that are plugged into different AC circuits in the household.
The commonest symptom of such is hum in the audio.

Audio can be point-to-multipoint (one sender, multiple receivers or
jacks) *if* the sending device has the ability to drive multiple
loads. Don't try this with composite or S-video, though - you'll
probably end up with a weak, unstable, or ghost-filled picture.

Running the cables and adding the connectors at one end after the
cable is in place, so that the holes can be as small as possible?

Yes, you can do this.

The other option is to install a standard-size switch/outlet box in
the wall at each end, and use a wall cover plate which has the
appropriate jacks on it. You can buy cover plates with such jacks
pre-installed, or a cover plate which accepts two or four or more jack
inserts (RCA, S-Video).

It was easy to run co-ax of whatever length I wanted, and then attach
a connector at the end, after I had pushed it through the holes in the
floors and walls. And to have splitters whereever there was another
tv, and RF amplifier-splitters whereever the signal got weak.

You can use an audio amplifier, isolation transformers, etc. to handle
the audio distribution problem.

For baseband (composite or S-video) you'll have trouble getting away
with a "branched" topology. You can't just use T-connectors or
passive splitters, as these will cause either impedance mismatches or
a decrease in video signal voltage which will mess up the picture.

I don't play all the tvs at once, but I have branches now for 8 tvs.
Doesn't that mean I need some "outboard" amplification, rather than
trying to play 2 or 3 of them at the same time just with the output
from the DVDR?

Yup. You'll need a video distribution amplifier - one which accepts
an incoming video signal, and produces independent buffered (isolated)
video outputs of the correct voltage. You'll then need to run a
separate cable from the distribution amplifier to each destination.

What you are considering is not a small project, I think. If you've
had difficulty soldering RCA plugs successfully, you're likely to find
the soldering of S-Video connectors to be a serious headache.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
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