Adding neutral wire to old coop apt?

Outlets (where you plug stuff in) aren't involved.

The fixture at the ceiling already has a neutral.

Where you're probably missing the neutral is at the switch. Two hot wires go from the fixture to the switch. No neutral was necessary when the wiring was done.

One option is to run a neutral from the fixture to the switch in the existing conduit. There may not be room in the conduit, though.

Better would be use dimmable CFLs and a dimmer that will work with them without a neutral. See http://www.lutron.com/PRODUCTS/STANDALONECONTROLS/DIMMERS-SWITCHES/DIVADIMMERSWITCH/Pages/Models.aspx

Dimmable CFLs suck rotten eggs; they most closely resemble on/off, not dim. Wait until standard-replacement LED bulbs are improved ... very soon.

Oh, and see if there's a good Insteon/x10 solution for you, although I think running a neutral in a 1950s building is not very expensive. I did so, using http://leaderelectric.com/index.html, and recommend them.