if you go to widows -> settings ->Plug in Manager is it listed there?
I had a similar problem. when I put the Ziva module in the maya folder in my c:/ drive, It would only load in maya if i ran Maya as an administrator. (this was on a work machine so i don't have permissions as a local user for lots of stuff)
you could try putting it in the maya modules folder in your documents. That seemed to work for me.