Hi Brian -
The Method API allows you to interact with the data in Method (such as retreiving a list of customers, or inserting an invoice). It isn't used to actually create a user interface.
To create a user interface in Method, it's done by creating and customizing screens directly in Method itself - no coding, just drag and drop.
If you are a coder - which I'm guessing you are seeing as you are on the MethodAPI forum and are working with dynamic XML - you may not like the sound of making a screen using drag and drop. But when it comes to the UI, this is where I recommend you go, it's what users are used to, and what makes it easy for users to import an app that you make. There are options available to you, such as creating links on Method pages call on other pages, Method web window objects (which are iframes), or buttons that call external webservices.........but the more you design your UI using Method, the better.
If you need heavy complex calculations or processing, I would suggest building as much UI as you can within Method, and then clicking a button that calls an external webservice to do the heavy processing.
I hope that's a good start. Let me know if you need clarification.
Paul