By default Vista fills the initial view of the start menu with often used applications. The order of those applications may change based on how frequent an application is started. One can make sure, that an application stays permanently in the start menu.
Just Right click on an application in the start menu and select Pin to Start Menu.
This even works for any .EXE file in the Windows Explorer! Right clicking and selecting Unpin from Start Menu detaches an application from the start menu.