Cannot Install JDK
Solution 1:
Go to regedit and then go to HKEY_CLASSES_ROOT\Installer\Products\ look for Development kit and delete the key
Solution 2:
You probably just need to set your "PATH" environment variable as explained in the Java 6.0 Installation Notes for your platform. This will cure the problem for running "java" and "javac" from the command line and for running Eclipse.
You should be able to confirm that Java is installed by going to the relevant Windows control panel (whose name temporarily escapes me) and looking for the JDK / JRE in the list of installed software.