If your custom class resides within your ASP.NET webapp, either in an assembly (dll) within your "bin" folder or as source code within the "App_Code" directory, then just put the name of your custom class in place of "System.Collections.Hashtable" in the example I gave. If your custom class resides within an assembly (dll) within the Global Assembly Cache (GAC), then you need to specify the fully-qualified class name, including assembly name, version, etc.
The only other "trick" to know is that when accessing class properties, you must use .NET IL syntax, not C# property syntax. This is as simple as appending "get_" or "set_" to the property name (which is what the C# compiler does). In the Hashtable example, notice that I access the Item property using "get_Item()".
You can find more information in Section 4.1.2 of the following document:
Integrating CFML with ASP.NET
Just to be clear, this integration of CFML and ASP.NET is only available with BlueDragon.NET and not with Adobe ColdFusion.