JSI Tip 6339. The Winnt32.msi package prompts for a Product ID when you use Non-Select Media?

Microsoft Knowledge Base Article 246617 contains the following summary:

When you use the Winnt32.msi package to upgrade a computer and you are using non-Select media that requires a product ID (PID), you need to provide a PID by using an Unattend.txt file. This involves creating an Unattend.txt file and modifying the Winnt32.msi package to include this file.