|This is the XP forum. You listed Vista as your OS. I'll assume you're asking about XP.|
You can't install XP without a product key so you must have either entered it during the installation, or it's built in to the repair disc. Since you mentioned a 30 day limit, you're probably asking about activation. If your installation is legal, all you need to do is activate online. If it's illegal, do a google search for "make xp 100% genuine".