Exchange 2007 only adds 64-bit components in a 64-bit install, when you install Exchange it will register CDOEX.DLL which will replace CDOSYS.DLL and be used when you instantiate CDO.Message. So you will see CDO.Message pointing to "C:\Program Files\Common Files\Microsoft Shared\CDO\CDOEX.DLL" in the 64-bit registry and you will see CDO.Message pointing to "C:\WINNT\SysWow64\cdosys.dll" in the 32-bit registry. If your application is a 64-bit process it will load up CDOEX.DLL when you instantiate CDO.Message. If your application is a 32-bit process it will load up CDOSYS.DLL when you instantiate CDO.Message.
After installing 64-bit Exchange 2007 you may notice that 32-bit scripts and applications get a "Library not found" error when using CDOSYS. This appears to be a side effect of registering the 64-bit CDOEX.dll. To resolve the issue simply open a 32-bit instance of cmd.exe from the SysWow64 directory and run "regsvr32 cdosys.dll" to re-register the 32-bit CDOSYS.