hook_menu

Here's the code in system_modules_submit() - the function called when admin/modules is saved - that skips over flushing caches if no modules are enabled or disabled:

It works. Count how many parts to the menu path there are (text between slashes) and put that number in as a page argument in the array provided for this. (This actually means to grab the /next/ piece of the menu path to use , because the system's counting starts at zero.

Passing Arguments to Form Functions through hook_menu()
http://drupal.org/node/457782