Oracle Database Discussions

I'm struggling with trying to install Oracle 11g on Windows 7. I've downloaded the installation files from OTN and extracted them to a folder on my PC. But when I try to run the Oracle Universal Installer, it pops up the cmd window, waits for a couple of seconds and then pops up a Java Virtual Machine window with the error 'Could not find the main class. Program will exit' and then terminates.
I've searched metalink and google and tried all sorts of things including installing jre (1.6) as well as setting TEMP and JRE_LOCATION variables as suggested but without success.
Could someone please suggest what might be going wrong here.
Thanks.