>I can remove IE 5.5 and go back to 5.0, but I have 2 questions about that.
1. How the heck do I do that?

You will see "Internet Explorer 5.5" or something similiar in the add/remove list.

>2. What if this is being caused by something he did or acidently signed up for somewhere?

Is there any indication what the application might be? I once had some silly app install itself like this too. Damned if I can remember how I got rid of it.

> Will reverting back to 5.0 fix this?

I am reaching for straws. Let's see what happens.