The drives do not show in iMovie 10. The storage model is completely different (and more flexible).
To move events from a library to a new library, create a new library (File - Open Library - New) and specify its name and location. Then select and copy to it all the events and projects you want to put in it This way you won't break any links to external media.
Alternatively to move a whole library, selct the library in the libraries pane go File - Consolidate Library media (this ensures that any external media are copied to the library package). You can then move this library to its new location using Finder. iMovie won't find it by itself - the first time you want to open it you will ahve to File - Open Library - Other and navigate to its new location.
I hope this helps
Apple is dragging us screaming into the future. As usual with a radical update, some functionality disappears either because its getting out of date and will be gone for good (eg support for DVDs, Anamorphic video) or because the new version is not yet ready and it will reappear in a future version. The same thing happened when Final Cut Pro X was first introduced. iMovie 10 and FCP 10.1 have quite similar user interfaces.