NOTE: This applies 32bit dlls and require site application pools to be configured for 32bit.

It's by habit that we simply browse to the directory where a DLL is placed usually "C:\Windows\system32" and type "regsvr32 mynewobject.dll" only to find that doesn't work or you receive an error.

To register a dll in the 64bit Windows follow these steps:

1. Copy the DLL to the following folder, "C:\Windows\syswow64\".
2. Open command prompt, type "cd C:\Windows\syswow64\"
3. Type "regsvr32 mynewobject.dll" and press enter.


You should receive a message saying that the component was "registered successfully". This should work when trying to register a 32bit dll in 64bit windows with 32bit application pools.

To regisister 64bit DLL's use the standard "regsvr32 mynew64bitobject.dll".

References:
Explanation of Regsvr32 usage and error messages