When you "execute" an asp page that create an object, the DLL is loaded
in memory by IIS. Then this DLL is not unloaded.
To unload it you must stop and then restart IIS admin services.
you can write a little batch file like :

:------------------------------------------
net stop "Microsoft SMTP service"
net stop "World Wide Web Publishing Service"
net stop "FTP Publishing service"
net stop "IIS Admin Service"

net start "IIS Admin Service"
net start "World Wide Web Publishing Service"
net start "FTP Publishing service"
net start "Microsoft SMTP service"
:-------------------------------------------

(remove line of service you're not using.

The second point is that when you open a page in visual interdev, and in
the page, you have code like : set toto =
server.createobject("XXXX.XXX") the DLL containing your class is loaded
in memory, so that the editor can help you to write call finishing your
calls...
To unload the dll, just close the asp page in visual interdev editor...

An other problem is when you use MTS. The component is loaded the first
time you use it and you must "shut down server processes" to release
your components and so the activeX dll...

Hope this help...

Stephane CHEVALIER