more home wiring: where's my neutral?

I've got a 25 year old house, whose light switches I'm converting over to a powerline protocol called INSTEON (see www.smarthome.com; for
purposes of this question, it's very similar to the old X10 protocol).
Two of the bedrooms are on one circuit breaker (the whole rooms: lights, outlets, the whole shebang). Each room has a single switch controlling the lights in that room. I pulled a light switch out this evening, planning to replace it, when I saw there was no neutral in the junction box (the INSTEON switches require both hot and neutral). At first I expected to find neutral in the wall behind the box (I was guessing they had, for some reason, routed hot through the box and to the switch while leaving neutral unbroken), but then realized that what went in the box was a single piece of three-conductor wire, with black used for hot, white for switched, and ground not connected.
So... before I start digging the junction box out, what are my odds of finding neutral somewhere in the vicinity? More generally, I'm having a hard time imagining why someone would wire the ceiling light fixture and not have power and neutral come from the same place! So, before I get myself in trouble, how did they likely wire it?
Thanks in advance,
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You would find neutral in the same outlet that is onthe same circuit breaker.
i
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Neutral is probably up in the light fixture. It is perfectly acceptable to run the hot and neutral to the light fixture, then run a hot and switched hot to the light switch. Ground wires tended to get ignored when running to a switch only. Not the best but it was often done.
If you dig around and find a neutral, it is unclear if you would find the correct neutral. It might work if you found a different neutral but the loads would be unbalanced. Not to mention unsafe if you wanted to work on the OTHER circuit.
Joe Pfeiffer wrote:

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Joe Pfeiffer wrote:

Most likely the feeder with hot & neutral went to the light fixture junction box. The neutral was wired to the fixture and the hot went out to the switch. The switched hot back from the switch was wired to the fixture. Very common.
H --------/\------------ S N ------- L ----------
Bob
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It's called a switch leg. Power should actually come in on the white and leave the switch on the black. There is no neutral in the box or probably anywhere near. This is normal and probably half the light switches in the world are wired this way.
Code prohibits you finding a neutral from some other location. All circuit conductors should come from the same cable.
You could replace the switch leg with a piece of 3 wire (don't count the ground in a cable with uninsulated ground) from the light to the switch and abandon the 2 wire you have to gain a neutral for your switch.
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The term is "switch leg".....
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