This is one of my first Salesforce hacks; this trick will learn you how to load an hidden S-Control on every Salesforce page:

My S-Control is “hidden” using a style sheet command. The “hint” that there is an embedded S-Control is a message on the sidebar that reads “Field Level Help Enabled”.

Basically, you write an S-Control, then create a custom home page component of type “HTML”, choose the “show HTML” checkbox, and type in the following code:

<iframe src="/servlet/servlet.Integration?lid=XXXXXXXXXXX" style="display: none"></iframe>

After you save this change and add it to the home page sidebar, it will execute on any page that includes the sidebar. The “lid” parameter is the ID of the S-Control to execute.