To permanently set your JAVA_HOME
Environment Variable under Windows to the JDK directory you've mentioned do the following:
Click Start, right click on Computer and select properties (you can also hold down the windows key and press the pause/break key).
Click on Advanced system settings on the left.
Click the Environment Variables button on the bottom.
Click the New... button below the System variables window.
Enter the following:
Variable name: JAVA_HOME
Variable value: C:\jdk1.6.0_23\
Click Ok, Ok, Ok, and close the system control panel you opened in step 1
Close and re-open your command prompt.
If you are using Eclipse then skip the steps above and do the following:
Click on the Window menu and choose Preferences.
Expand the Ant entry on the left and click on Runtime
Click on Global Entries in the Classpath tab on the right.
Click Add External JARs...
Navigate to C:\jdk1.6.0_23\lib and select tools.jar then click open.
Hit ok to Close the preferences Window.
In your situation however your best bet would probably be to simply append C:\jdk1.6.0_23\bin
to your PATH
env var using my first set of instructions above as a rough guideline.