Delphi – Unable to see certain HKEY_LOCAL_MACHINE entries in RegEdit

The problem is that you are trying to create a key not read it. You should be able to read values from HKLM just fine on Vista if you use the appropriate API.

RegistryKey myKey = Registry.LocalMachine.OpenSubKey(
  @"Software\MyCompany\MyAppName", 
  false);

Notice the false parameter in the above. This has the effect of opening the key in a read only mode. This is the default setting for OpenSubKey but I prefer to be explicit (mainly because I can't ever remember the default).

This is an excellently put question, +1 (Why is it community wiki, it deserves points!)

In general, there are a set of rules (which [as you've run into] will vary over time) which control whether UAC [and thus implicitly Registry] virtualization are in play.

Some salient parts of the Registry Virtualization rulesets documentation in MSDN are:

1. [as jeffamaphone says] if the manifest has a requestedPrivileges/requestedExecutionLevel set, it's turned off. You dont seem to have ruled out adding a manifest, so can you please indicate why this won't work for you? (You say "I haven't been able to do that in C# V2" - there is an Add Item option to add an application manifest file, and that's available in VS2005)
2. if the exe is running 64 bit, its off by default
3. if it's not an interactive process (such as a service, or hosted in IIS etc.), it's off

If you're not in a position to influence any of the above, which is the ideal, and you thus want to detect whether UAC virtualisation applies in the current context, use this answer to a what might at first not appeat to be a related question. (Obviously you'd still need to decide whether it applies to the specific key you're operating on, which is a moving target which you obviously wouldnt want to implement code that needs to track changes if it can at all be avoided - but in most cases it should be relatively clear.)