Detect whether MS Office installed is 32bit or 64bit by using registry

From TechNet article on 64-bit editions of Office 2010:

If you have installed Office 2010 including Microsoft Outlook 2010, Outlook sets a registry key named Bitness of type REG_SZ on the computer on which it is installed. The Bitness registry key indicates whether the Outlook 2010 installation is 32-bit or 64-bit. This may be useful to administrators who are interested in auditing computers to determine the installed versions of Office 2010 in their organization.

• Registry path: HKEY_LOCAL_MACHINE\Software\Microsoft\Office\14.0\Outlook
• if you have installed Office 2013 then use this Registry path: HKEY_LOCAL_MACHINE\Software\Microsoft\Office\15.0\Outlook
• Registry key: Bitness
• Value: either x86 or x64

and elsewhere in the same article:

Starting with Office 2010, Outlook is available as a 32-bit application and a 64-bit application. The version (bitness) of Outlook that you choose depends on the edition of the Windows operating system (32-bit or 64-bit) and the edition of Office 2010 (32- or 64-bit) that is installed on the computer, if Office is already installed on that computer.

Factors that determine the feasibility of installing a 32-bit or a 64-bit version of Outlook include the following:

• You can install 32-bit Office 2010 and 32-bit Microsoft Outlook 2010 on a supported 32-bit or 64-bit edition of the Windows operating system. You can install the 64-bit version of Office 2010 and 64-bit Outlook 2010 only on a supported 64-bit operating system.
• The default installation of Office 2010 on a 64-bit edition of the Windows operating system is 32-bit Office 2010.
• The bitness of an installed version of Outlook is always the same as the bitness of Office 2010, if Office is installed on the same computer. That is, a 32-bit version of Outlook 2010 cannot be installed on the same computer on which 64-bit versions of other Office 2010 applications are already installed, such as 64-bit Microsoft Word 2010 or 64-bit Microsoft Excel 2010. Similarly, a 64-bit version of Outlook 2010 cannot be installed on the same computer on which 32-bit versions of other Office applications are already installed.

Extending Morten's answer, I did this in Wix 3.6

     <Component Directory="INSTALLLOCATION">
        <File Id="msvcp100.dll_x64" Source="$(var.x64)\msvcp100.dll" KeyPath="yes" />
        <Condition><![CDATA[VersionNT64]]></Condition>
     </Component>
     <Component  Directory="INSTALLLOCATION">
        <File Id="msvcp100.dll_x86" Source="$(var.x86)\msvcp100.dll" KeyPath="yes" />
        <Condition><![CDATA[Not VersionNT64]]></Condition>
     </Component>