Found at
http://www.canucky.net/2007/03/18/how-to-switch-to-windows-vista-64-bit-painlessly.html
1.. Click on the Start button.
2.. Click on “All Programsâ€, and then click on “Accessoriesâ€.
3.. Right click on “Command Prompt†and click “Run as administratorâ€.
4.. When User Account Control prompts you for consent, click on “Continueâ€.
5.. In the Command Prompt window, type “%windir%\system32\unregmp2.exe
/SwapTo:64″ (without the quotes) and then press Enter.
6.. In the Command Prompt window, type “regedit†(without the quotes).
7.. In the left hand side of the Registry Editor window, navigate to
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\App
Paths\wmplayer.exe
8.. Create a back up of the settings in this key just in case you wish to
switch back to the 32-bit Windows Media Player for whatever reason.
9.. Set the value for the (Default) key to “%ProgramFiles%\Windows Media
Player\wmplayer.exe†(include the quotes).
10.. Set the value for the Path key to “%ProgramFiles%\Windows Media
Player†(do not include the quotes).