Dan,
o.k., I think I understand now.
When I open Aperture, I see my old iPhoto events in the main panel labeled Projects.
You have opened you iPhoto Library as Aperture Library in Aperture. There is no need to import your iPhoto Library, and it is impossible to do so. Aperture will hid ethe curret library that you are using.
You can start to work with your iPhoto photos right from where you are. Click on one of the projects, and you will see all your iPhoto photos as images in the Aperture projects.
However, when I try to import a project to work on it (by pressing the large Import arrow at the top left), I am presented with a new screen with gray panels that contain file structurs at the bottom center (looks like a Finder).
This import panel will allow you to import additional files and folders, but not the library that you are currently browsing, for you would be importing the library into itself.
Again, I apologize for using incorrect terminology. Does this make the situation clearer?
No reason to apologize - a transit from one paradigma and diction to another is always confusing, and Apple does not provide a guide for switching between these applications.
What is it, that you want to do? You can either open your iPhoto library in Aperture, like you are doing now, and continue from there, without any import necessary; or you could create a new Aperture library and import your iPhoto library into Aperture (with "File > Import > Library", then select your iPhoto Library). This will create a new Aperture library, containing a duplicate of your iPhoto Library. But this would only be necessary, if you have several iPhoto libraries that you want to unite. I hope this is clear, if not, please ask back!
Regards
Léonie