How to add a hyper-link to an action button in Open Office.org Presentation?
This is from Oracle's OpenOffice Help TNT blog:
The last step here is applicable only if you want to link to a document. If you want to link to a web page, enter the url in the "URL" field, right below where you selected the action.
Now you've got to leave design mode (button in the form controls toolbar) for the button to work.