For the life of me, I can't install the JDK on Windows Vista. I keep getting the error, "This Software Has Already Been Installed on Your Computer. Would you like to reinstall it?" Problem is, it's evidently not on my computer, since I can't a) run Eclipse - I get "Could Not Find Java SE Runtime Environment" or b) Find any reference to Java from the command line when typing java -version - I get "Error opening registry key 'Registry/JavaSoft/Java Runtime Environment." Any ideas?
Go to regedit and then go to HKEY_CLASSES_ROOT\Installer\Products\ look for Development kit and delete the key
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.
First check your PATH environment variable (my computer-> properties->Advanced, environment variables) to see what java executable is in your path. If it is something obsolete, clear it up. second, as @Stephen C says, un-install your version that is apparently in your computer. Goto control panel-> Add/remove programs -> JRE/JDK then un install.
Then try downloading latest Java 2 standard edition installer