You can install Vista with no product key and have 30 days to evaluate it.
Boot from the DVD and start the installation
Select the Language, Time and Currency, and Keyboard
Click on Next
Click on Install Now
Don't enter a Product Key
Uncheck Automatically activate Windows when I'm online
Click on Next
Click on No to confirm you do not want to enter a product key
Highlight the version of Vista you want to install
Check that it is the same edition you have purchased (if you want to enter in a product key at a later time).
Click on Next
Check accept the license and terms
Click on Next
Install a clean copy and continue as with a regular install.
Windows Vista tips Troubleshooting
