Sounds like a good idea on the surface, but I don't think it's the way to go. If the DB is that complicated, formal training would be better. You can always make your own help guide with custom menus.
You may want to explore tool tips that you can attach to fields, objects and buttons to guide users.
Install onTImerScript could set a timer on the window that would perform a script on a regular interval. That script could update a match field in the table that matches to a different record and thus a field or portal could display different text very so many minutes.
onTimerScript would be good if you wanted it to change every 30 seconds (any time frame). You could also use onLayoutEnter to just change the tip every time you enter the layout. I would use a related table (match field) and then insert on to the layout using a merge field. I would just use these tips for information purposes (Features available, for example: Did you know you could Print a report to PDF? ) not to teach a user how to use the feature.