Run a form automatically when opening dynamics AX + 2012

Create a new  menu item for the form which form you want run opening dynamics AX.

Call that method as shown in below

new MenuFunction(menuitemDisplayStr(YourMenuItemName), MenuItemType::Display).run();

Place this code to Info.startupPost() (if you want it to start when the client starts) 
                                   or 
Info.workspaceWindowCreated() (if you want it to start every time new workspace is opened).

Startup message + ax 2012

1. Open the Configuration Utility (Start > Control Panel > Administrative Tools > Microsoft Dynamics AX Configuration Utility).
2. Verify that the currently open configuration target and configuration are the ones you want to modify.
3. On the General tab, in the Startup message box, enter the message you want to display, and then click OK.
   When the client is started, the text displays in a message box, with an OK button below.

Set a startup message for Microsoft Dynamics AX client

To set a startup message

Following are the two methods which are useful to show start-up message at the beginning of AX 2009.
1. Update the Client configuration Utility option.
Microsoft Dynamics AX Configuration Utility (client) -> Genereal Tab -> Field "Startup Message"

2. If you have to add the custom message as per users name at the beginning of AX 2009 then update the following code in Classes---> Info class---> StartUpPost method.
void startupPost()
{
UserInfo UserInfo;
select Name from UserInfo where UserInfo.id==curUserId();
info('Welcome to '+UserInfo.name);
}