Why can't I upgrade to the final version of Windows XP from an interim build?

A. Although you can technically upgrade from an interim build of XP to the final version, Microsoft has restricted the upgrade path for certain builds. However, I know of two methods for circumventing these restrictions.

Method 1
This method is the more complicated of the two. It involves modifying a file in your boot partition before you reboot.

1. Run setup from the final XP image. If you receive a message stating that you can't upgrade this version of Windows, you need to perform a fresh install by selecting Fresh Install.
2. Continue with the installation, and choose the same Windows directory for the installation that you want to upgrade.
3. When setup prompts you to reboot, press Escape to manually reboot later, and setup will return you to the Windows shell.
4. The directory $win_nt$.bt in the root of your boot partition (which is typically C:) should contain a file named winnt.sif. Open this file in Notepad.
5. Look for the line that reads winntupgrade=no, and change the winntupgrade value to yes.
6. Save the file, and reboot your system.

Method 2
XP contains a Program Compatibility Wizard that you typically use to set up a virtual environment that mimics another version of Windows for programs that won't run under XP. Using this wizard, you can fool the final installation into thinking that you're running Windows 2000.

1. Start the Program Compatibility Wizard (go to Start, Programs, Accessories, and click Program Compatibility Wizard).
2. Select 'I want to use the program in the CD-ROM drive' and click Next.
3. Select Microsoft Windows 2000 and click Next.
4. Continue to click Next as appropriate to complete the wizard.