Hi astublif,
in NAV 5.0 there is a slightly different way of applying entries after posting them than in the newer releases. When you get into the "Apply Entries" window, you first have to select the entry which should act as the applying entry. Usually you set the cursor on the desired entry and use the menu "Application->Set Applying Entry" or Shift+F9. This record will be shown in the head of the form now. Afterwards you select the entries you want to apply to (F9 for select/deselect), distribute the amount, what you need to do. Afterwards you need to post the application.
This should be documented in the online help... but caution: if you're using a newer release of binaries ("technical update"), then the online help is most likely from the newer version.
with best regards
Jens