I just wrote this blog to help all those who might be facing problems while upgrading from Netbeans 6.1 to Netbeans 6.5.
Installing Netbeans was never a problem. But, I never knew it would be a problem while upgrading it. I just uninstalled the previous version, downloaded the new version & ran it. But it didn't found the compatible jdk on its own, even though I had jdk 1.6 already installed on my system. Even when I tried to specify the path explicitly, it showed an error message "an unknown error occurred while validating the path". I tried several things from uninstalling jdk to downloading the latest version. But nothing helped. Even running Net beans 6.1 setup again showed the same problem.
I was clueless. Then googling helped & i found this article. The problem still remained unknown to me but I found the solution. The solution was to delete the all the Netbeans (all of them were usually starting from '.')related files present in the folder C:\User\your_user_name. The setup identified the installed jdk version on its own this time and finally I was able to install Netbeans 6.5 on my system.