Not quite sure what exactly you mean...
You don't 'make dlls valid' for PHP at all, don't know what you mean by that. You can't just use a DLL as a PHP script or something... You can call and access DLLs under Windows with PHP by using the 'w32api functions' which are covered in the PHP manual.
In general, the idea behind COM DLLs is that they can be written in any language, and use a standard RPC kinda system so that anything else can call them.
If you just want your PHP script to end with *.dll, you should look at ForceType for Apache, not sure where you'd look for IIS servers.