As Richard Walters stated, registering a COM object does not copy it anywhere. Usually I am lazy and rather than looking up long GUIDs in REGEDIT, I search for the DLL's name using the Find feature.
Since you mentioned PowerShell, can I assume you are trying to use Javascript within the Windows Script Host? If so, knowing what the exception is might help. An example on how to do this though:
var xml = new ActiveXObject("Microsoft.XMLDOM");
xml.load("foo.xml");
Of course replace Microsoft.XMLDOM with information from your COM object.
The equivalent PowerShell would be:
$xml = New-Object -ComObject Microsoft.XMLDOM
$xml.load("foo.xml")