RE: Need help to customize enterprise portal web part pages in sharepoint designer 2010 ?
For your first question,
1. You can find (Applications) pages inside AOT > Web Files > Page definition. (Example :The Project home page is EPProject )
2. You can find the resources in AOT > Web Files > Static Files
3. If you want to Edit Controls. (Example : Editing the Timesheet Grid control). You can find it in AOT > WebFiles > Web Controls. You can Edit them in Visual Studio. Here you can find the application proxy (C# Code) that would connect to AX to retrieve App data. In VS you can expose the other Classes, Form and tables in the control too.
For your second question,
Page definition usually contains the code for the
1. Overall layout
2. Web Part zones
You can edit them directly in AOT or Put them in VS and get help with Intellisense for editing.
With respect to Web Controls, you can edit them only in VS.
You can also directly edit the files which are stored in <Program Files>\Common Files\Microsoft Shared\Web Extensions \14\Templates\Layouts . I would not recommend this as AOT would not know the changes and would overwrite in the next deployment.
P.S If you want your business users to change it, it is always advised to add more webpart zones, so that they can edit the page and customize them. If its more of a development thing, you can follow the above.
Regards,
Saravanan | Enterprise Architect | My Blog