When I select some polygons on my model and choose a subprojection in the UV editor, the polygon's vertices are stretched to the dimensions of the texture:



The actual dimensions of the polygons on the model when viewed from the XY orthographic view is this:



Is there a way that I can get the polygons to come in at their actual proportions, instead of having to mess around with scaling them in the UV editor so that the textures won't be badly stretched?

umm, i'm not sure what's going on there. Which subprojection are you using? I usually use planar subprojection, which works fine for me. Or does this happen with all subprojections. I probably won't be able to give an answer, as i try to stay far, far away from the texture side of things.
OFF TOPIC: what is the new avatar?

I was using YZ planar (object oriented), and this happens with all subprojections.

OFF-TOPIC: The avatar is hands Mine and my girlfriends, at a birthday party.

I'm not sure if this works all the time, but what I do is open up the texture editor, click the cube icon up the top and select 'best fit'. Sometimes though, the polygons will be stretched out all of the way, so you'll have to manually resize it.