Summarize:

You will be changing the setup file from a 16-bit installer to a 32-bit installer. In order to do this, you will need a packaging software such as WinInstall LE (freeware). In order to create the setup file, you will need to install Photoshop and WinInstall LE on a machine that is compatible. You MUST perform these steps on a compatible machine. You can either use a Virtual PC (as outlined above), or another computer that has a 32-bit version of Windows. Running on a clean install on a virtual machine is preferred because there are no conflicting programs. Start Discover mode, which has a magnifying glass icon in the toolbar. This will open the Discover Wizard. WinInstall will take a before and after snapshot of your system files when you perform an installation. It will take this information and create a new 32-bit installer that can work on 64-bit systems.  You will need to create a name for the new installer, as well as a path for the new installer. WinInstall will ask which drives you want to have scanned. You should indicate the hard drive that you are installing Photoshop on. After configuring the Discovery mode, WinInstall will analyze your system. This may take a few moments. Once Discovery mode is running, start the installation of Photoshop. Install it as you would on your 64-bit machine, including all of the options you would pick. Wait for the installation to complete. Once the installation is complete, run Discovery mode in WinInstall again. You will be given the option to run the After mode or start a new Discovery. Select After to create a new snapshot of your system. WinInstall will look at the Before and After, and build a new installation package. Move the new installer onto your 64-bit machine. Run the installer and install Photoshop as normal.
Download a packaging software. Open WinInstall. Install Photoshop. Run Discover mode again. Copy the new installer.