This is, in the main, just a quick note to myself! When editing the registry on a Windows x64 based computer, but the program that will read those registry settings is a 32 bit application then you need to change the location that you edit to the “Wow6432Node” rather than the usual location.
Note that when blogs and other technical articles write down a registry key they do not often mention that the registry location you need to change is not what they have written down!
For example, there is a problem in the Windows 7 RC release in which Internet Explorer 8 does not show some webpages resulting in an error “A webpage is not responding on the following website:” (see http://support.microsoft.com/kb/970858). The registry key describes setting the hangresistance value, but as Internet Explorer is a 32 bit application you need to set the hangresistance value at HKLM\SOFTWARE\Wow6432Node\Microsoft\Internet Explorer\MAIN\ and not at HKLM\SOFTWARE\Microsoft\Internet Explorer\MAIN\.
If you follow the advice in the Microsoft support article KB970858 then it will not fix the problem on a 64 bit machine. You need to edit the Wow6432Node value instead.
There is an x64 version of Internet Explorer installed, but the common one that people use is the 32 bit version – if you use both, set both registry keys.