As Sergey said, COM DLLs need to be registered the same as ActiveX controls. However, if you are using Windows 2003/SP3 or later OS you can create an "Assembly Manifest" file. It is an XML file that sits along side your EXE (or you can embed it into your EXE if you know how) and allows you to use a COM DLL or ActiveX without registereing it.

For more info, check out this web site: http://msdn2.microsoft.com/en-us/library/aa374219.aspx