By default Windows XP uses the C:\Program Files directory as the base directory into which new programs are installed. But there might be times when you want a new program to be installed in another directory or may be another drive, instead of the default location. Almost all programs allow you to choose where you want to install the program, at the time of installation.
But if you find yourself changing the installation location every time you install a new program, you might probably want to change the default location itself so that Windows automatically installs new programs in the drive/directory of your choice. You can do this with a simple Registry Hack.
Run the Registry Editor by going to Start > Run, type ‘regedit‘ and press Enter.
Navigate to the following location:
Look for the value named ProgramFilesDir. By default,this value will be C:\Program Files. Edit the value to any valid drive or folder and Windows XP will use that new location as the default installation directory for new programs.