Microsoft Dynamics AX 2009 EP introduced the asp.net web framework. In the prior versions, the web user interface logic was defined entirely in X++. Asp.net framework has lots of great benefits , the big ones being AJAX capabilities, rich out of the box controls and the power of .net and asp.net for customization, extensibility, performance and reliability.
Here are the topic related to migrating existing X++ web forms to asp.net EP user controls.
1. Use the SysEPWebFormConverter to move the Web form datasources to the dataset and the user control. For simple cases, it should automate everything.
2. Refer to the migrating code pattern document and move the code as needed to the dataset X++ methods or to C# in user control as suggested by this document
3. Refer to the Microsoft Dynamics AX 2009 EP dev cook book for general development tips-n-tricks