In the process of setting up a 64bit Server 2008 box, I ran into a little issue trying to convince IE which tool to use when I want to view the source of a web page or document. All of the "documentation" out on the web states that you need to modify the following registry key:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\View Source Editor\Editor Name
But for some bizarre reason, it wasn't working for me. After beating my head around a bit and some fruitless searches, I finally brought out Process Monitor so I could watch and see exactly what registry key IE was looking at (gee, I should have done that to begin with). As it turns out, they decided to walk to the Wow6432 node instead, in support of that whole multiple version thing: This way you can have both a 32bit and a 64bit version installed and their settings don't tromp on each other.
So, if you are setting your own application, I suggest modifying both of the following nodes if you are running a 64-bit OS:
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\View Source Editor\Editor Name]
[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Internet Explorer\View Source Editor\Editor Name]