Skip the product ID:
One of the very first steps in setting up Windows Vista is this prompt to enter a product ID. If you're familiar with Windows XP, you probably enter this reflexively. But in Vista RC1 (and probably in the final version as well), you can leave the product ID box blank. If you do this, you'll see a stern warning that says you better input that ID if you know what's good for you. You can safely skip it if you know you have (or will have) a legitimate product ID but it isn't at hand, or if you are planning to evaluate Windows Vista for 14 days or less.
