How to publish a variable name or library in the global "namespace" of Drupal from a module

Hello all.

I want to do a simple thing : give access to a library from drupal code (most notably php code in some very special pages through php filter).

But I don't know the proper way to do it.

Is there a hook for that ?

Or does the fact of creating a global variable in a dot.module suffice to make that variable availiable in all of Drupal code when the module is registered ?

My library is luckily very simple to interface since a single function in a single file/module needs to be make available to Drupal.

Or maybe somebody could point me to a similar module that simply "publish to Drupal" a third party api.

I tried to look up some code in third party adaptation libraries but since those libraries tend to do lots of "glue code" to give a better integration to Drupal they are not of much use in my case.

I also had a look at the "libraries" module (http://drupal.org/project/libraries) but I would like to do the "simple thing" i.e. a module with the library in a subdirectory of it, before messing with the /site/all/library path and the "libraries" module API (http://drupal.org/node/320562). Unless somebody has a sample of code using it to feed me :)

Thanks a lot for you time and help.