The type of user account is not related to whether or not you have activated Vista. There are two types of user accounts on Vista, Administrator and Standard User. Only Administrator accounts can install programs. You can tell what kind of account you have by going to the Control Panel and selecting User Accounts and Family Safety and then User Accounts. You should see your account type on the right side of the window under the account name.
Okay, yeah, I'm under admin account. I haven't had any trouble downloading until now. It's just this game.