Hi Mark, module development must not be complex at all. You can reuse all your existing knowledge. The main difference is that module are enhanced ascx controls, and no aspx pages.

Simple steps for displaying a grid view, splitted into two idenpended steps to separate issues of the gridview with the dotnetnuke integration. Once you are getting familar with module dev., you will start diirectly within DotNetNuke

1) Without DotNetNuke:

• Write your gridview and all you logic in one example.ascx.
• Create an aspx page, but no logic inside, just drag and drop your user control inside
• Ensure that everything is working as expected.

2) Integration into DNN

• Create a folder "example" in dotnetnuke/desktopmodules
• Copy your example.ascx and example.ascx.vb into that folder
• Open example.ascx.vb and change the "inherits" line to inherits DotNetNuke.Entities:Modules.PortalModuleBase
• Open you DNN in browser, go to Host->Module Definitions. 
  Click on Create a new Module.
  Enter "example" as the module name, folder name and friendly name. Click on create
  Enter "example" inside "New definition", click on add definition
  Click on Add control, choose desktopmodules/example/example.ascx as source. Click on Update
• Create a new page/tab. Add the module "example".
• Enjoy

3) Examine the framework, study the source of some core modules to learn the befits of the platform.

Even as lead of the iframe module I won't encourage using Iframe for your issue.