Better Javascript help for noobs

Hi,

I could use some basic how-to's on making an existing Javascript work inside Drupal. The documentation on this topic jumps all over the place and gets into way too much detail for my simple application. I don't need a comprehensive course on how the API works, or how to write a Javascript -- all I need to do is reference an existing script on a page and have it work the way it did outside Drupal. (If it helps, the script is "overlib.js" and I would want it to work regardless of theme - although theme level would be OK if that simplifies it.)

Is there someone who could post some simple, step-by-step instructions for incorporating an existing Javascript into a page?

Thanks in advance.
m.e.