64 Bit System Registry

The registry in 64-bit versions includes both 32-bit and 64-bit keys.Both are under one umbrella.You can view or edit both 64-bit and 32-bit registry keys and values by using the default 64-bit version of Registry Editor.

Where the 32-bit keys are displayed :-

They are displayed here:-HKEY_LOCAL_MACHINE\Software\WOW6432Node

How to open the 32-bit version of Registry :-
Start >Run>In the Open box, type %systemroot%\syswow64\regedit, and then click OK.

What will you do before opening 32/64 Bit registry version?
Before opening 32 Bit registry you must close the 64 Bit registry and vice-versa.

Role of -m Switch:-

but using -m switch one can start the 32 bit version registry. For example, if the 64-bit version of Registry Editor is already running, type %systemroot%\syswow64\regedit -m in step 2 to start the 32-bit version of Registry Editor.

Reference:-How to View the System Registry By Using 64-Bit Versions of Windows
http://support.microsoft.com/kb/305097/