Sold my house (it's a good thing) and moved into an apartment (that's the plan) where I'm not allowed to have an antenna. Ha!

My shack is next to a window and I've got a big ole tree right there.  I'm thinking two halves of an OCFD (wire only) slid out the top of the window at > 90* angle should be ok.  

Also, if I pass the insulated wire between the frame and window (think top pane of double hung) is my window going to become coupled to the antenna?

ETA: I have a 16'9" whip and mount - how can I stick this out the window and make it work on 20M? (my main question is, how do I create a ground/counterpoise when I'm on the second floor?)

Tell them you are part of Homeland Securities 'Civilian Defense Team'.

What I found in my apartment was living so close to so many wall warts and un-terminated CATV lines was that it wasn't worth the effort of trying to operate here, solid S9+ noise on everything (even 2m and 440)

I was in an apartment for a year. I had a second story apt and a balcony with a steel rail and a tall tree just off the balcony. A mag mount for VHF/UHF stuck to the railing and a wire launched up in the tree worked for me. I used a piece of wire inside for the ground counterpoise routed along the edge of the floor. Noise was a real issue on HF though. Almost not worth the effort. VHF/UHF FM worked fine though. At one point I had a small tripod and a "loaded" vertical on the balcony but it didn't work too well.
An end fed tossed up in your tree may work too. No counterpoise needed IIRC.

I once lived in an apartment in Phoenix. It was in a prestigious area but I hated it. Too much (audio) noise for me and having any antennas was out of the question. I ended up installing a mobile HF radio and an antenna on my Jeep. I had a blast with it.

That's what I was going to suggest, also.  

I was thinking about that too - I already have the 9:1 balun made for my QRP 40/30/20 CW machine so I might throw a 20M (1/2 wave) in the tree and see what happens.

Thanks to all for ruining my day by the way with all the stories of TOO MUCH NOISE

Alexloop on a tripod.

On the inside of the window, run one or two wires (depending on window location) against the junction of the ceiling and walls. Go at right angles to the whip as far as possible, then along the other wall(s) until you have about a quarter wavelength of wire.. Mechanically, it might be better to mount the base of the whip on the bottom ledge of the window and use some monofilament fishing line from the top of the window to the top of the whip to support it. Move the counterpoise wire down accordingly.

As mentioned before, your big problem is probably going to be noise from consumer electronics. I was in a condo for a couple of years in the early '80s and even then the noise from fluorescent lights and TV sets was horrific.

The good news is that I was able to be heard on pskreporter last night, albeit with -12 and less.  But that's with the 16' mast laying on the floor in the middle of the apartment.  I'm going to rig up a mount today or tomorrow so that I can throw it out the window when desired with some counterpoise wires inside, and then note the lengths for the band(s) I want to operate on.

The bad news is that I didn't make contact and the noise level was horrible (S7+) but it does seem to work.  

Regardless - I get to operate this year!

If not for noise you could probably do well on 20M with the full-size whip.   On a second story if you could manage a couple somewhat drooping radials somehow it would really work great.   But one just dangling like a tail probably wouldn't be bad either so long as it's all well above ground.

Just the noise, it can be bloody hell.

Another option, utilize the tree and run a EARCHI type endfed via a 9:1 un-un.   These are not a true end fed but really an OCF that's fed at a different impedence point than the traditional design, and probably somewhat more immune to the local noise.   I have been experimenting with this a bit lately.   By the Original EARCHI design it's not a solid performer but 20' or so of feedline (laying on the ground) as counterpoise makes it easy to tune only because of ground loss.   On a second story that's hard to do so instead you choke off the feedline and use a separate counterpoise, which must be tuned as half of the OCF that it really always was.   But then, after all of the effort you will have something that should perform.

Another option, feed a wire to the tree and a dangling tail via an SGC or radio specific auto coupler.   With that you are again in the realm of a vertical in nature and noise issues and also you'll need to choke the shit out of the feedline but if you are fortunate and somehow manage to not have a huge noise problem you will gain much from the ease of operation.   I actually use something similar to this at home most of the time.   I have a pretty good mass of metal that is connected to the ground side because it's there, but it isn't really necessary.

First I'm going to try to craft a 'slide under' mount for the mast.  I bought a mirror mount for mine and I'm going to grab a 6"x12" piece of steel that I can hold in place with the window (double hung) with a few strategic bends and then attach the mirror mount to it.  We shall see.

If that causes too much trouble it's going to be an EFHW as I can throw that out the window at a moments notice (and there's a big tree right out side my window!)

Alrighty then - I have purchased 100' of 14ga THHN to use as counterpoise within the apartment - I'm think 6 CP's @ 16.66' each?
Also, I would guess that I want as short a piece of RG8x from the radio to the antenna, correct?

This is all assuming I expect to run only 20m. I know I can shorten the whip to the appropriate length if I go up in frequency, what do I have to do to the counterpoise wires?  Can I create a single counterpoise for each band I want to run - one each for 20/15/10?

The endfed uses the coax as counterpoise, but I have had a lot of luck on remote sites with as little as 12 ft of coax between the antenna and radio.

Sorry, not doing the endfed yet (I'll probably end up there though).
This is with the 16'9" MFJ extendable whip

I have learned one thing, my radio is not a fan of on 20M with just a 16'9" whip w/o counterpoise wires - I get 5W out (self protection I'm sure).  I'll be adding counterpoise tonight

ETA: However, that didn't stop me from making 2 QSO's last night

Strange, but then the feedline could be an unfortunate length, at least with respect to it's function as a counterpoise.   So then, adding a counterpoise the right length might bring it down where it needs to be, at the same time choking the feedline at the feed point.