changing jdk in eclipse

I am trying to update my eclipse to work with a jdk and not a jre. I followed the instruction in this forum , also search google for answers but for some reason it still don't work.

I try'ed going to preferences ->java->install jre's , removing the old jre from there and using the path for the jdk.

also try'ed going to project properties -> java build path -> jre system libraries -> edit-> workspace default jre.it also says there i'm using jdk.

I even try'ed adding to the ini file the next path C:\Program Files\Java\jdk1.6.0_31\bin\javaw.exe

but when i try'ed deploying my program to app engine i get the next message : Unable to update app: Cannot get the System Java Compiler. Please use a JDK, not a JRE.

my eclipse version is juno 4.2 and my jdk version is 1.6.0_31 I don't know what else i need to change. I even uninstall my older jre from my computer but eclipse still don't work with the jdk ( although it recognize it )

I'm out of idea's ... anyone could help me please ??

this is my ini file :

    -startup
    plugins/org.eclipse.equinox.launcher_1.3.0.v20120522-1813.jar          
    --launcher.library
    plugins/org.eclipse.equinox.launcher.win32.win32.x86_1.1.200.v20120522-1813
    -product
    org.eclipse.epp.package.jee.product
    --launcher.defaultAction
    openFile
    --launcher.XXMaxPermSize
    256M
    -showsplash
    org.eclipse.platform
    --launcher.XXMaxPermSize
    256m
    --launcher.defaultAction
    openFile
    -vmargs
    -Dosgi.requiredJavaVersion=1.5
    -Dhelp.lucene.tokenizer=standard
    -Xms40m
    -Xmx512m
    -vm
    C:\Program Files\Java\jdk1.6.0_31\bin

thanks for the help