I can answer your question only somewhat.
Lightroom does have an auto-import function, although I'm not sure if it will serve your purposes. See the screencast at
http://screencast.com/t/g0myXRxO. I don't actually have iPhoto installed on my Mac, so I can't test to make sure it works. It looks like Lightroom might move (instead of copy) all of the photos, making them inaccessible in iPhoto. I'd make a backup of some kind before you try this.
As for seeing photos in iPhoto with the Lightroom changes, that can't be done without exporting from Lightroom. Those photos with the Lightroom changes don't actually exist until export: all Lightroom stores is the original image and the math required to re-apply those changes. Sometimes thumbnail previews are stored as well, but those seem to be inside the Lightroom catalog; you don't want to be mucking around in there.
You could look into using Aperture instead of Lightroom. The simplest thing, though, is to just use one program and stick with it exclusively.