Good news and bad news. The bad news is there isn't a way to create ActiveX Server project in CVI 5.5. You can create DLL's with type library information, but not an object-based COM or ActiveX interface.
Now, for the good news, you can do it in CVI 6.0. A new feature of CVI 6.0 is a ActiveX Server wizard that makes creating and maintaining ActiveX Server projects as easy as possible. To upgrade to Measurement Studio 6.0 (which includes CVI 6.0), go to http://www.ni.com/upgrade. I attached a white paper that comes with CVI 6.0 that shows how creating ActiveX servers in CVI 6.0 works.
Best Regards,
Chris Matthews
National Instruments