Is there a way to block Java in Window's Registry?

Have you tried a HOSTS file? You could use that to block the game's pages. But, if the other person knows a thing or two about HOSTS files, it wouldn't be enough.

just set up a user account, and dont tell them the password....

well then set them up with another account with limited access!

what do you mean at work? i dont know what policy your work has, but you should NEVER let anyone use your work account, anything they do will be logged, so that means that if they go onto the wrong sort of sites, its YOUR ass on the line..

hmm, u dont need admin access, you misunderstood, at work everything you do is logged by someone higher up with admin rights such as the IT Tech.. they will report to someone higher if they find that you play java games too much therefore getting YOU in trouble, not the person that used your account... use windows key + L to lock the computer.

if you do not have admin you wont be able to change the registry at work anyway, you can only secure yourself at home by creating another account and not handing out your password, same at work always lock the pc and make sure you do not hand it out.

at my work place i am the admin, after someone kept hold of a laptop at home for a long period, we were asked to check why, the only thing we found was that the person in question had bought lots of ebay stuff... and we only use very simple monitoring software.

They won't.