How To Build Custom Configuration Section In App.Config File

I am trying to build custom configuration section in my app.config file. I am using the following as my example: [URL]. According to this article, I am supposed to inherit from the ConfigurationSection class, add the desired section to my app.config file, and then specify a "configSections" declaration in the app.config file to identify the section and the class that should process it. My problem is that I cannot get the class loader to load my class for processing the section.

If I follow the example and set up my "configSections" as:
<configSections>
<section name="MyStuff.Configuration"
type="MyStuff.MyConfigurer"
allowLocation="true"
allowDefinition="Everywhere" />
</configSections>

I get the following error:
Could not load type 'MyStuff.MyConfigurer' from assembly 'System.Configuration, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'.

I think the error is telling me it can't load my class from the System.Configuration DLL and that makes sense; the class is in my application code. So how do I tell it to look in my application code to find the class? Do I have to put my class in its own DLL to get this to work? As an alternative approach, is there some way I can just find the section in the application configuration and process the XML myself? The app.config file is the ideal location for this information. Also, this would be easier for me than going through all of these contortions to do what should be a relatively easy operation.