debug and modify android core app ( like settings ) on eclipse, window

First of all, you need compiled AOSP(http://source.android.com/) which API Level you want to use.

In my case, i'm using API 15 and vbox_x86 Env.

in your AOSP_HOME

@bgpark:ics$ . build/envsetup.sh
@bgpark:ics$ lunch vbox_x86-eng

@bgpark:ics$ make -j12

I think you already know this one.

Select Add Library by right mouse click

and make user library with System Library check option.

add some jar files.

for example, we need 2 shared jar for Settings project.

add guava_intermediates\classes.jar by add External jar and change reference order.

now you can build without any problems.

You will need this article for run your core app with appropriate authority.
http://stoned-android.blogspot.com/2012/01/sign-your-apk-with-platform-key-for.html