Maybe I can help you, if it isn't to late, I've made some screensavers myself whit visual basic.Net 2003 and 2005.
If you want to have a box of some sort showing advertisements, one at the time and when it chances you can see the first one being pushed away by the other one.
Then you could try to do this by making some pictureboxes, each one has a different advertisement, and then let one be shown at the time. And when the advertisement should chanc let the first one move to the bottom of the screen, until his position is no longer on the screen, and while the first one does this you let the second one come from somewhere above the screen enter the screen.
If you do not understand, what I'm trying to tell, just let me know and I could try to explain it again.
If you would like to see the sreensavers I've made whit visual basic .NET 2003 you can visit my site:
my-apps.tk
The screensavers I've made whit vb.NET 2005 aren't one that site (jet).