VB Code:
  1. Public Function GetAppPath()
  2.     GetAppPath = IIf(Right(App.Path, 1) = "\", App.Path, App.Path & "\")
  3. End Function
  4.  
  5. 'Usage:
  6.  
  7. Msgbox GetAppPath

This will get the app.path including the "\" on the end, i know it's an simple function but i use it many times in my apllications.

A time ago i always used:
Exec App.path & "\test.exe", that will work only if your app is not in the root of an drive.