What may be news to you, however, is that you can easily extend the 30-day Windows Vista grace period to 120 days. No hacks required. This is an official, supported operation directly from Microsoft.
To extend the grace period another 30 days, simply start a command prompt as Administrator, and issue this command:
Reboot for the change to take effect, and voila, you have 30 more days. You can only extend three times, so the total grace period for a Vista evaluation is 120 days.Continue At Source