I am trying to install the ADT plugin for Eclipse. However, after I have went to \"Install New Software...\" and entered the plugin location https://dl-ssl.google.com/android/ec
I've faced with the same problem before. In my case this was a problem that I was working under the proxy. I think you also work behind a proxy.
I've solved this problem in the following way. Find the SDKManager.exe and run it. In this program find proxy configuration and fill it there. Then from this program try to update your SDK (maybe this will require you to restart this program).
I do not know why but Eclipse proxy configuration is not working in case of Android ADT.
P.S. You have to use JDK 6 (or 5), not JDK 7!!!