how to used the registered activeX control at server side in ASP or ASP.NET web page?

In ASP.Net, you would just set a reference to the COM object in your project

Adding the reference will create a COM Interop [^] assembly that you can then use from your .Net code

In classic ASP, you can use the Server.CreateObject [^] method and pass the prog ID of your COM component.

You would do this in your particular ASP page that needs to use the functionality, not in the Global.asa

--EDIT -- Follow these steps

1) Open your project in visual studio
2) On References, right click and choose 'Add Reference'. The dialog is displayed
3) Switch to COM tab, find you COM DLL and double click to add reference. The Interop DLL is added to your references
4) In your 'code behind', you can now use your COM. Add a using statement

using MyComLibrary;

5) Create and use your objects

MyCOMClass item = new MyCOMClass();
item.DoSomething();