Shoutbox

If your admin has disabled access to the registry and write access to the program files directory, you may be stuck.

If you know (or know someone who does) the admin pass, then you can usually right click the installer and go "Run As..." which should allow you to install the plugin normally.

If you have access to both folders, you could maybe use another tool to extract the files out the installer and add a line or two in the registry, although I'm not sure if all plugins need access to it.